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It has been my object in these pages to present the 
life of each astronomer in such detail as to enable the 
reader to realise in some degree the man's character and 
surroundings ; and I have endeavoured to indicate as 
clearly as circumstances would permit the main features 
of the discoveries by which he has become known. 

There are many types of astronomers — from the star- 
gazer who merely watches the heavens, to the abstract 
mathematician who merely works at his desk; it has, 
consequently, been necessary in the case of some lives to 
adopt a very different treatment from that which seemed 
suitable for others. 

"While the work was in progress, some of the sketches 
appeared in Good Words. The chapter on Brinkley has 
been chiefly derived from an article on the " History of 
Dunsink Observatory," which was published on the occa- 
sion of the Tercentenary celebration of the University of 
Dublin in 1892, and the life of Sir William Eowan 
Hamilton is taken, with a few ^alterations and omissions, 
from an article contributed to the Quarterly Review on 

viii PREFACE. 

Grraves' life of the great mathematician. The remaining 
chapters now appear for the first time. For many of the 
facts contained in the sketch of the late Professor Adams, 
I am indebted to the obituary notice written by my friend 
Dr. J. W. L. Glaisher, for the Royal Astronomical Society ; 
while with regard to the late Sir George Airy, I have a 
similar acknowledgment to make to Professor H. H. 
Turner. To my friend Dr. Arthur A. Rambaut I owe 
my hearty thanks for his kindness in aiding me in the 
revision of the work. 

R. S. B. 

The Obseevatoey, Cambridge. 
October, 1895. 


Inteodtjction 1 

Ptolemy 7 

copeenicus 30 

Tycho Beahe 44 

Galileo 07 

Kepler 96 

Isaac Newton 116 

Flamsteed 147 

Halley . . . . . . . . . . . .162 

Beadley . . . . . . . . . . .187 


Laplace 219 

Beinkley 233 

John Heeschel 247 

The Eael of Rosse 272 

AiEY 289 

Hamilton 303 

Le Veeeiee 335 

APAMg ,,,,,,,,,,,, 354 



The Oeservatoey, Q-eeenwich Frontispiece 

Ptolemy 9 

Ptolemt's Planetaey Scheme 24 

,, Theoey op the Movement op Maes .... 26 

Thorn, feom an Old Print 32 

Copernicus 33 


Explanation of Planetary Movements . . . . . .41 

Tycho Brahe 47 

Tycho's Cross Staff .50 

„ "New Star" Sextant of 1572 51 

,, Trigonio Sextant 52 

,, Astronomio Sextant ... .... 53 

,, Equatorial Armlllary 54. 

The Great Augsburg Quadrant 55 

Tycho's "New Scheme of the Terrestrial System," 1577 . 56 

Uraniboeg and its Grounds 57 

Ground-Plan of the Observatory 5g 

The Observatory of Ueaniborg, Island of Hven ... 59 
Effigy on Tycho's Tomb at Prague. By permission of Messrs. 

A. & C. Black gj 

Tycho's Mural Quadeant, Ueaniboeg 53 

Galileo's Pendulum ^0 

Galileo ^3 

The Villa Aecetei 32 

Facsimile Sketch of Lunar Surface by Galileo . . .87 

Crest of Galileo's Family 94 

Kepler's System of Regular Solids 100 

Kepler ............ 103 

Symbolical Ee presentation qts the Planetary System . .106 



The Commemoeation of the Rudolphine Tables . . .111 

"WooLSTHOEPE Manor . . .117 

Trinity College, Cambeidge 121 

Diagram of a Sunbeam . . ~ 123 

Isaac Newton 126 

Sir Isaac Newton's little Eeflectoe 129 

,, ,, Sun-Dial 132 

,, ,, Telescope 135 

,, ,, Astrolabe 138 

,, „ Sun-Dial in the Royal Society . . 146 

Flamsteed's House . . 151 

Flamsteed 155 

Halley 167 

Greenwich Obseevatoey in Halley' s Time . . . .185 

7, New Kjng Steeet, Bath. From a Photo, by John Poole, Bath 204 

William Heeschel 206 

Caroline Herschel 207 

Street View, Heeschel House, Slough \ From / 209 

Garden View, „ " f Photographs by I 212 

Observatory, ,, " ( "^^^^ ^ Saunders, j 216 

The 40-Foot Telescope, ,, j Eton \ 217 

Laplace 227 

The Observatory, Dunsink. From a Photograph by W. Law- 
rence, Dublin 239 


Sir John Herschel 253 

Nebula in Southern Hemisphere 256 

The Cluster in the Centaur . . . . . . .259 

Obseevatory at Feldhausen 262 

Granite Column ,, 265 

The Earl or Rosse 273 

Birr Castle. From a Photograph by W. Lawrence, Dublin . 275 

The Mall, Paesonstown. ,, „ . 277 

LoED Rosse's Telescope. ,, „ . 281 

Roman Catholic Chuech, Paesonstown. ,, . 285 

AiEY. From a Photograph by E. P. Adams, Greenwich . . 293 

Hamilton 313 

Adams 357 

The Obsejiyatort, Cambridge •. , i i , , , 3QQ 


Of all the natural sciences there is not one which offers 
such sublime objects to the attention of the inquirer as 
does the science of astronomy. From the earliest ages the 
study of the stars has exercised the same fascination as 
it possesses at the present day. Among the most primitive 
peoples, the movements of the sun, the moon, and the 
stars commanded attention from their supposed influence 
on human affairs. 

The practical utilities of astronomy were also obvious 
in primeval times, Maxims of extreme antiquity show 
how the avocations of the husbandman are to be guided 
by the movements of the heavenly bodies. The positions 
of the stars indicated the time to plough, and the time to 
sow. To the mariner who was seeking a way across the 
trackless ocean, the heavenly bodies offered the only 
reliable marks by which his path could be guided. There 
was, accordingly, a stimulus both from intellectual curiosity 
and from practical necessity to follow the movements of 
the stars. Thus began a search for the causes of the 
ever-varying phenomena which the heavens display. 

Many of the earliest discoveries are indeed prehistoric. 
The great diurnal movement of the heavens, and the 



annual revolution of the sun, seem to have been known in 
times far more ancient than those to which any human 
monuments can be referred. The acuteness of the early 
observers enabled them to single out the more important 
of the wanderers which we now call planets. They saw 
that the star-like objects, Jupiter, Saturn, and Mars, with 
the more conspicuous Yenus, constituted a class of bodies 
wholly distinct from the fixed stars among which their 
movements lay, and to which they bear such a superficial 
resemblance. But the penetration of the early astro- 
nomers went even further, for they recognized that 
Mercury also belongs to the same group, though this 
particular object is seen so rarely. It would seem that 
eclipses and other phenomena were observed at Babylon 
from a very remote period, while the most ancient records 
of celestial observations that we possess are to be found 
in the Chinese annals. 

The study of astronomy, in the sense in which we under- 
stand the word, may be said to have commenced under 
the reign of the Ptolemies at Alexandria. The most 
famous name in the science of this period is that of 
liipparchus, who lived and w^orked at Ehodes about the 
year 160 B.C. It was his splendid investigations that first 
wrought the observed facts into a coherent branch of 
knowledge. He recognized the primary obligation which 
lies on the student of the heavens to compile as complete 
an inventory as possible of the objects which are there to be 
found. Hipparchus accordingly commenced by undertak- 
ing, on a small scale, a task exactly similar to that on which 
modern astronomers, with all available appliances of meri- 
dian circles, and photographic telescopes, are constantly 


engaged at tlie present day. Pie compiled a catalogue 
of the principal fixed stars, whicli is of special value to 
astronomers, as being the earliest work of its kind which has 
been handed down. He also studied the movements of the 
sun and the moon, and framed theories to account for 
the incessant changes which he saw in progress. He found 
a much more difficult problem in his attempt to interpret 
satisfactorily the complicated movements of the planets. 
With the view of constructing a theory which should give 
some coherent account of the subject, he made many 
observations of the places of these wandering stars. How 
great were the advances which Hipparchus accom- 
plished may be appreciated if we reflect that, as a pre- 
liminary task to his more purely astronomical labours, he 
had to invent that branch of mathematical science by 
which alone the problems he proposed could be solved. 
It was for this purpose that he devised the indis- 
pensable method of calculation which we now know so 
well as trigonometry. Without the aid rendered by this 
beautiful art it would have been impossible for any really 
important advance in astronomical calculation to have been 

But the discovery which shows, beyond all others, that 
Hipparchus possessed one of the master-minds of all time 
was the detection of that remarkable celestial movement 
known as the precession of the equinoxes. The inquiry 
which conducted to this discovery involved a most pro- 
found investigation, especially when it is remembered that 
in the days of Hipparchus the means of observation of the 
heavenly bodies were only of the rudest description, and 
the available observations of earlier dates were extremely 


scanty. We can but look with astonishment on the 
genius of the man who, in spite of such difficulties, was 
able to detect such a phenomenon as the precession, and 
to exhibit its actual magnitude. I shall endeavour to 
explain the nature of this singular celestial movement, 
for it may be said to offer the first instance in the history 
of science in which we find that combination of accurate 
observation with skilful interpretation, of which, in the 
subsequent development of astronomy, we have so many 
splendid examples. 

The word equinox implies the condition that the night 
is equal to the day. To a resident on the equator the 
night is no doubt equal to the day at all times in the 
year, but to one who lives on any other part of the earth, 
in either hemisphere, the night and the day are not 
generally equal. There is, however, one occasion in 
spring, and another in autumn, on which the day and 
the night are each twelve hours at all places on the earth. 
When the night and day are equal in spring, the point 
which the sun occupies on the heavens is termed the 
vernal equinox. There is similarly another point in 
which the sun is situated at the time of the autumnal 
equinox. In any investigation of the celestial movements 
the positions of these two equinoxes on the heavens are 
of primary importance, and Hipparchus, with the instinct 
of genius, perceived their significance, and commenced to 
study them. It will be understood that we can always 
define the position of a point on the sky with reference 
to the surrounding stars. No doubt we do not see the 
stars near the sun when the sun is shining, but they are 
there nevertheless. The ingenuity of Hipparchus enabled 


him to determine the positions of each, of the two equi- 
noxes relatively to the stars which lie in its immediate 
vicinity. After examination of the celestial places of 
these points at different periods, he was led to the 
conclusion that each equinox was moving relatively to 
the stars, though that movement was so slow that twenty- 
five thousand years would necessarily elapse before 
a complete circuit of the heavens was accomplished. 
Hipparchus traced out this phenomenon, and established 
it on an impregnable basis, so that all astronomers have 
ever since recognised the precession of the equinoxes as 
one of the fundamental facts of astronomy. Not until 
nearly two thousand years after Hipparchus had made 
this splendid discovery was the explanation of its cause 
given by Newton. 

From the daj^s of Hipparchus down to the present hour 
the science of astronomy has steadily grown. One great 
observer after another has appeared from time to time, 
to reveal some new phenomenon with regard to the 
celestial bodies or their movements, while from time to 
time one commanding intellect after another has arisen 
to explain the true import of the facts of observations. 
The history of astronomy thus becomes inseparable from 
the history of the great men to whose labours its 
development is due. 

In the ensuing chapters we have endeavoured to sketch 
the lives and the work of the great philosophers, by 
whose labours the science of astronomy has been created. 
We shall commence with Ptolemj^, who, after the founda- 
tions of the science had been laid by Hipparchus, gave 
to astronomy the form in which it was taught throughout 


tlie Middle Ages. We shall next see the mighty revo- 
lution in our conceptions of the universe which are 
associated with the name of Copernicus. We then pass 
to those periods illumined by the genius of Galileo and 
]^ewton, and afterwards we shall trace the careers of 
other more recent discoverers, by whose industry and 
genius the boundaries of human knowledge have been 
po greatly extended. Our history will be brought down 
late enough to include some of the illustrious astronomers 
who laboured in the generation which has just passed 


The career of the famous man whose name stands at the 
head of this chapter is one of the most remarkable in the 
history of human learning. There may have been other 
discoverers who have done more for science than ever 
Ptolemy accomplished, but there never has been any 
other discoverer whose authority on the subject of the 
movements of the heavenly bodies has held sway over the 
minds of men for so long a period as the fourteen cen- 
turies during which his opinions reigned supreme. The 
doctrines he laid down in his famous book, " The Alma- 
gest," prevailed throughout those ages. No substantial 
addition was made in all that time to the undoubted 
truths which this work contained. 'No important correc- 
tion was made of the serious errors with which Ptolemy's 
theories were contaminated. The authority of Ptolemy 
as to all things in the heavens, and as to a good many 
things on the earth (for the same illustrious man was 
also a diligent geographer), was invariably final. 

Though every child may now know more of the actual 
truths of the celestial motions than ever Ptolemy knew, 
yet the fact that his work exercised such an astonishing 
effect on the human intellect for some sixty generations, 


shows that it must have been an extraordinary produc- 
tion. We must look into the career of this wonderful 
man to discover wherein lay the secret of that marvellous 
success which made him the unchallenged instructor of 
the human race for such a protracted period. 

Unfortunately, we know very little as to the personal 
history of Ptolemy. He was a native of Egypt, and 
though it has been sometimes conjectured that he be- 
longed to the royal families of the same name, yet there 
is nothing to support such a belief. The name, Ptolemy, 
appears to have been a common one in Egypt in those 
days. The time at w^hich he lived is fixed by the fact 
that his first recorded observation was made in 127 a.d., 
and his last in 151 a.d. When we add that he seems to 
have lived in or near Alexandria, or to use his own 
words, "On the parallel of Alexandria," we have said 
everything that can be said so far as his individuality is 

Ptolemy is, without doubt, the greatest figure in ancient 
astronomy. He gathered up the wisdom of the philoso- 
phers who had preceded him. He incorporated this with 
the results of his own observations, and illumined it with 
his theories. His speculations, even when they were, as 
we now know, quite erroneous, had such an astonishing 
verisimilitude to the actual facts of nature that they 
commanded universal assent. Even in these modern days 
we not unfrequently find lovers of paradox who maintain 
that Ptolemy's doctrines not only seem true, but actually 
are true. 

In the absence of any accurate knowledge of the science 
of mechanics, philosophers in early times were forced to 


fall back on certain principles of more or less validity, 
which they derived from their imagination as to what the 
natural fitness of things ought to be. There was no geo- 
metrical figure so simple and so symmetrical as a circle, 


and as it was apparent that the heavenly bodies pursued 
tracks which were not straight lines, the conclusion obviously 
followed that their movements ought to be circular. There 
was no argument in favour of this notion, other than the 


merely imaginary reflection that circular movement, and 
circular movement alone, was "perfect/^ whatever *' per- 
fect " may have meant. It was further believed to be 
impossible that the heavenly bodies could have any other 
movements save those which were perfect. Assuming 
this, it followed, in Ptolemy's opinion, and in that of 
those who came after him for fourteen centuries, that all 
the tracks of the heavenly bodies were in some way or 
other to be reduced to circles. 

Ptolemy succeeded in devising a scheme by which the 
apparent changes that take place in the heavens coidd, so 
far as he knew them, be explained by certain combina- 
tions of circular movement. This seemed to reconcile 
so completely the scheme of things celestial with the 
geometrical instincts which pointed to the circle as the 
type of perfect movement, that we can hardly wonder 
Ptolemy's theory met with the astonishing success that 
attended it. We shall, therefore, set forth with sufficient 
detail the various steps of this famous doctrine. 

Ptolemy commences with laying down the undoubted 
truth that the shape of the earth is globular. The proofs 
which he gives of this fundamental fact are quite satis- 
factory ; they are indeed the same proofs as we give to- 
day. There is, first of all, the well-known circumstance 
of which our books on geography remind us, that when 
an object is viewed at a distance across the sea, the lower 
part of the object appears cut off by the interposing 
curved mass of water. 

The sagacity of Ptolemy enabled him to adduce another 
argument, which, though not quite so obvious as that 
just mentioned, demonstrates the curvature of the earth 


in a very impressive manner to anyone wlio will take the 
trouble to understand it. Ptolemy mentions that travel- 
lers who went to the south reported, that, as they did so, 
the appearance of the heavens at night underwent a 
gradual change. Stars that they were familiar with in the 
northern skies gradually sank lower in the heavens. The 
constellation of the Great Bear, which in our skies never 
sets during its revolution round the pole, did set and rise 
when a sufficient southern latitude had been attained. 
On the other hand, constellations new to the inhabitants 
of northern climes were seen to rise above the southern 
horizon. These circumstances would be quite incom- 
patible with the supposition that the earth was a flat 
surface. Had this been so a little reflection will show 
that no such changes in the apparent movements of the 
stars would be the consequence of a voyage to the south. 
Ptolemy set forth with much insight the significance of 
this reasoning, and even now, with the resources of modern 
discoveries to help us, we can hardly improve upon his 

Ptolemy, like a true philosopher disclosing a new truth 
to the world, illustrated and enforced his subject by a 
variety of happy demonstrations. I must add one of 
them, not only on account of its striking nature, but also 
because it exemplifies Ptolemy's acuteness. If the earth 
were flat, said this ingenious reasoner, sunset must neces- 
sarily take place at the same instant, no matter in what 
country the observer may happen to be placed. Ptolemy, 
however, proved that the time of sunset did vary greatly 
as the observer's longitude was altered. To us, of course, 
this is quite obvious ; everybody knows that the hour of 


sunset may haye been reached in Great Britain while it is 
still noon on the western coast of America. Ptolemy 
had, however, few of those sources of knowledge which 
are now accessible. How was he to show that the sun 
actually did set earlier at Alexandria than it would in a 
city which lay a hundred miles to the west ? There was 
no telegraph wire by which astronomers at the two places 
could communicate. There was no chronometer or watch 
which could be transported from place to place ; there 
was not any other reliable contrivance for the keeping 
of time. Ptolemy's ingenuity, however, pointed out a 
thoroughly satisfactory method by which the times of 
sunset at two places could be compared. He was ac- 
quainted with the fact, which must indeed have been 
known from the very earliest times, that the illumination 
of the moon is derived entirely from the sun. He knew 
that an eclipse of the moon was due to the interposition 
of the earth which cuts off the light of the sun. It was, 
therefore, plain that an eclipse of the moon must be a 
phenomenon which would begin at the same instant from 
whatever part of the earth the moon could be seen at 
the time. Ptolemy, therefore, brought together from 
various quarters the local times at which different ob- 
servers had recorded the beginning of a lunar eclij)se. 
He found that the observers to the west made the time 
earlier and earlier the further away their stations were 
from Alexandria. On the other hand, the eastern ob- 
servers set down the hour as later than that at which the 
phenomenon appeared at Alexandria. As these observers 
all recorded something which indeed appeared to them 
simultaneously, the only interpretation was, that the more 


easterly a place the later its time. Suppose there were a 
number of observers along a parallel of latitude, and each 
noted the hour of sunset to be six o'clock, then, since the 
eastern times are earlier than western times, 6 p.m. at 
one station a will correspond to 5 i*.M. at a station e 
sufficiently to the west. If, therefore, it is sunset to the 
observer at a, the hour of sunset will not yet be reached 
for the observer at b. This proves conclusively that the 
time of sunset is not the same all over the earth. We 
have, however, already seen that the apparent time of 
sunset would be the same from all stations if the earth 
were flat. When Ptolemy, therefore, demonstrated that 
the time of sunset was not the same at various places, he 
showed conclusively that the earth was not flat. 

As the same arguments applied to all parts of the 
earth where Ptolemy had either been himself, or from 
which he could gain the necessary information, it fol- 
lowed that the earth, instead of being the flat plain, 
girdled with an illimitable ocean, as was generally sup- 
posed, must be in reality globular. This led at once to a 
startling consequence. It was obvious that there could 
be no supports of any kind by which this globe was sus- 
tained ; it therefore followed that the mighty object must 
be simply poised in space. This is indeed an astonish- 
ing doctrine to anyone who relies on what merely seems 
the evidence of the senses, without giving to that evidence 
its due intellectual interpretation. According to our 
ordinary experience, the very idea of an object poised 
without support in space, appears preposterous. Would it 
not fall? we are immediately asked. Yes, doubtless it 
could not remain poised in any way in which we try the 


experiment. "We must, however, observe that there are 
no such ideas as upwards or downwards in relation to 
open space. To say that a body falls downwards, merely 
means that it tries to fall as nearly as possible towards 
the centre of the earth. There is no one direction along 
which a body will tend to move in space, in preference to 
any other. This may be illustrated by the fact that a 
stone let fall at New Zealand will, in its approach towards 
the earth's centre, be actually moving upwards as far as 
any locality in our hemisphere is concerned. Why, then, 
argued Ptolemy, may not the earth remain poised in 
space, for as all directions are equally upward or equally 
downward, there seems no reason why the earth should 
require any support ? By this reasoning he arrives at the 
fundamental conclusion that the earth is a globular body 
freely lying in space, and surrounded above, below, and 
on all sides by the glittering stars of heaven. 

The perception of this sublime truth marks a notable 
epoch in the history of the gradual development of the 
human intellect. No doubt, other philosophers, in grop- 
ing after knowledge, may have set forth certain assertions 
that are more or less equivalent to this fundamental truth. 
It is to Ptolemy we must give credit, however, not only 
for announcing this doctrine, but for demonstrating it by 
clear and logical argument. We cannot easily project 
our minds back to the conception of an intellectual state 
in which this truth was unfamiliar. It maj^ however, be 
well imagined that, to one who thought the earth was a 
flat plain of indefinite extent, it would be nothing less 
than an intellectual convulsion for him to be forced to 
believe that he stood upon a spherical earth, forming 


merely a particle relatively to the immense sphere of the 

What Ptolemy saw in the movements of the stars led 
him to the conclusion that they were bright points attached 
to the inside of a tremendous globe. The movements of 
this globe which carried the stars were only compatible 
with the supposition that the earth occupied its centre. 
The imperceptible effect produced by a change in the 
locality of the observer on the apj)arent brightness of 
the stars made it plain that the dimensions of the 
terrestrial globe must be quite insignificant in com- 
parison with those of the celestial sphere. The earth 
might, in fact, be regarded as a grain of sand, while the 
stars lay upon a globe many yards in diameter. 

So tremendous was the revolution in human knowledo-e 
implied by this discovery, that we can well imagine how 
Ptolemy, dazzled as it were by the fame which had so 
justly accrued to him, failed to make one further step. 
Had he made that step, it would have emancipated the 
human intellect from the bondage of fourteen centuries of 
servitude to a wholly monstrous notion of this earth's im- 
portance in the scheme of the heavens. The obvious fact 
that the sun, the moon, and the stars rose day by dav, 
moved across the sky in a glorious never-ending proces- 
sion, and duly set when their appointed courses had been 
run, demanded some explanation. The circumstance that 
the fixed stars preserved their mutual distances from year 
to year, and from age to age, appeared to Ptolemy to 
prove that the sphere which contained those stars, and on 
whose surface they were believed by him to be fixed, re- 
volved completely around the earth once every day. He 


would thus account for all the phenomena of rising and 
setting consistently with the supposition that our globe 
was stationary. Probably this supposition must have 
appeared monstrous, even to Ptolemy. He knew that the 
earth was a gigantic object, but, large as it may have 
been, he knew that it was only a particle in comparison 
with the celestial sphere, yet he apparently believed, and 
certainly succeeded in persuading other men to believe, 
that the celestial sphere did actually perform these move- 

Ptolemy was an excellent geometer. I He knew that 
the rising and the setting of the sun, the moon, and the 
myriad stars, could have been accounted for in a different 
way. If the earth turned round uniforml}^ once a day 
while poised at the centre of the sphere of the heavens, all 
the phenomena of rising and setting could be completely 
explained. This is, indeed, obvious after a moment's re- 
flection. Consider yourself to be standing on the earth 
at the centre of the heavens. There are stars over your 
head, and half the contents of the heavens are visible, while 
the other half are below jouv horizon. As the earth turns 
round, the stars over your head will change, and unless it 
should happen that you have taken up your position at 
either of the poles, new stars will pass into your view, 
and others will disappear, for at no time can you have 
more than half of the whole sphere visible. The observer 
on the earth would, therefore, say that some stars were 
rising, and that some stars were setting. We have, 
therefore, two totally distinct methods, each of which 
would completely explain all the observed facts of the 
diurnal movement. One of these suppositions requires 


that the celestial sphere, bearing with it the stars and other 
celestial bodies, turns uniformly around an invisible axis, 
while the earth remains stationary at the centre. The 
other supposition would be, that it is the stupendous 
celestial sphere which remains stationary, while the earth 
at the centre rotates about the same axis as the celestial 
sphere did before, but in an. opposite direction, and with 
a uniform velocity which would enable it to complete one 
turn in twenty-four hours. Ptolemy was mathematician 
enough to know that either of these suppositions 
would suffice for the explanation of the observed facts. 
Indeed, the phenomena of the movements of the stars, so 
far as he could observe them, could not be called upon to 
pronounce which of these views was true, and which was 

Ptolemy had, therefore, to resort for guidance to indirect 
lines of reasoning. One of these suppositions must be 
true, and yet it appeared that the adoption of either was 
accompanied by a great difficulty. It is one of his chief 
merits to have demonstrated that the celestial sphere was 
so stupendous that the earth itself was absolutely insigni- 
ficant in comparison therewith. If, then, this stupendous 
sphere rotated once in twenty-four hours, the speed with 
which the movement of some of the stars must be executed 
would be so portentous as to seem well-nigh impossible. 
It would, therefore, seem much simpler on this ground to 
adopt the other alternative, and to suppose the diurnal 
movements were due to the rotation of the earth. Here 
Ptolemy saw, or at all events fancied he saw, objections of 
the weightiest description. The evidence of the senses 
appeared directly to controvert the supposition that this 


earth is anythiug but stationary. Ptolemy might, per- 
haps, have dismissed this objection on the ground that the 
testimony of the senses on such a matter should be en- 
tirely subordinated to the interpretation which our intelli- 
gence would place upon the facts to which the senses 
deposed. Another objection, however, appeared to him 
to possess the gravest moment. It was argued that if the 
earth were rotating, there is nothing to make the air par- 
ticipate in this motion, mankind would therefore be swept 
from the earth by the furious blasts which would arise 
from the movement of the earth through an atmosphere 
at rest. Even if we could imagine that the air were 
carried round with the earth, the same would not apply, 
so thought Ptolemy, to any object suspended in the air. 
So long as a bird was perched on a tree, he might very well 
be carried onward by the moving earth, but the moment 
he took wing, the ground would slip from under him at a 
frightful pace, so that when he dropped down again he 
would find himself at a distance perhaps ten times as 
great as that which a carrier-pigeon or a swallow could 
have traversed in the same time. Some vague delusion of 
this description seems even still to crop up occasionall}^ 
I remember hearing of a proposition for balloon travelling 
of a very remarkable kind. The voyager who wanted to 
reach any other place in the same latitude was simply to 
ascend in a balloon, and wait there till the rotation of the 
earth conveyed the locality which happened to be his 
destination directly beneath him, whereupon he was to let 
out the gas and drop down ! Ptolemy knew quite enough 
natural philosophy to be aware that such a proposal for 
locomotion would be an utter absurdity ; he knew that 


there was no such relative shift between the air and the 
earth as this motion would imply. It appeared to him to 
be necessary that the air should lag behind, if the 
earth had been animated by a movement of rotation. In 
this he was, as we know, entirely wrong. There were, 
however, in his days no accurate notions on the subject of 
the laws of motion. 

Assiduous as Ptolemy may have been in the study of 
the heavenly bodies, it seems evident that he cannot have 
devoted much thought to the phenomena of motion of 
terrestrial objects. Simple, indeed, are the experiments 
which might have convinced a philosopher much less 
acute than Ptolemy, that, if the earth did revolve, the air 
must necessarily accompany it. If a rider galloping on 
horseback tosses a ball into the air, it drops again into 
his hand, just as it would have done had he been re- 
maining at rest during the ball's flight ; the ball in fact 
participates in the horizontal motion, so that though it 
really describes a curve as any passer-by would observe, 
yet it appears to the rider himself merely to move up and 
down in a straight line. This fact, and many others simi- 
lar to it, demonstrate clearly that if the earth were endowed 
with a movement of rotation, the atmosphere surrounding 
it must participate in that movement. Ptolemy did not 
know this, and consequently he came to the conclusion 
that the earth did not rotate, and that, therefore, notwith- 
standing the tremendous improbability of so mighty an 
object as the celestial sphere spinning round once in 
every twenty-four hours, there was no course open except 
to believe that this very improbable thing did really 
happen. Thus it came to pass that Ptolemy adopted as 


the cardinal doctrine of his system a stationary earth 
poised at the centre of the celestial sphere, which stretched 
around on all sides at a distance so vast that the diameter 
of the earth was an inappreciable point in comparison 

Ptolemy having thus deliberately rejected the doctrine 
of the earth's rotation, had to make certain other entirely 
erroneous suppositions. It was easily seen that each star 
required exactly the same period for the performance of 
a complete revolution of the heavens. Ptolemy knew 
that the stars were at enormous distances from the earth, 
though no doubt his notions on this point came very far 
short of what we know to be the reality. If the stars 
had been at very varied distances, then it would be so 
wildly improbable that they should all accomplish their 
revolutions in the same time, that Ptolemy came to the 
conclusion that they must be all at the same distance, 
that is, that they must be all on the surface of a sphere. 
This view, however erroneous, was corroborated by the 
obvious fact that the stars in the constellations preserved 
their relative places unaltered for centuries. Thus it was 
that Ptolemy came to the conclusion that they were all 
fixed on one spherical surface, though we are not informed 
as to the material of this marvellous setting which sus- 
tained the stars like jewels. 

Nor should w^e hastily pronounce this doctrine to be 
absurd. The stars do appear to lie on the surface of 
a sphere, of which the observer is at the centre ; not only 
is this the aspect which the skies present to the untechni- 
cal observer, but it is the aspect in which the skies are 
presented to the most experienced astronomer of modern 


days. l^Q doubt he knows well that the stars are at the 
most varied distances from him ; he knows that certain 
stars are ten times, or a hundred times, or a thousand times, 
as far as other stars. Nevertheless, to his eye the stars 
appear on the surface of the sphere, it is on that surface 
that his measurements of the relative places of the stars 
are made ; indeed, it may be said that almost all the accu- 
rate observations in the Observatory relate to the places 
of the stars, not as they really are, but as they appear to 
be projected on that celestial sphere whose conception we 
owe to the genius of Ptolemy. 

This great philosopher shows very ingeniously that the 
earth must be at the centre of the sphere. He proves 
that, unless this were the case, each star would not appear 
to move with the absolute uniformity which does, as a 
matter of fact, characterise it. In all these reasonings we 
cannot but have the most profound admiration for the 
genius of Ptolemy, even though he had made an error 
so enormous in the fundamental point of the stability of 
the earth. Another error of a somewhat similar kind 
seemed to Ptolemy to be demonstrated. He had shown 
that the earth was an isolated object in space, and being 
such was, of course, capable of movement. It could either 
be turned round, or it could be moved from one place to 
another. We know that Ptolemy deliberately adopted the 
view that the earth did not turn round; he had then to in- 
vestigate the other question, as to whether the earth was 
animated by any movement of translation. He came to 
the conclusion that to attribute any motion to the earth 
would be incompatible with the truths at which he had 
already arrived. The earth, argued Ptolemy, lies at the 


centre of the celestial sphere. If the earth were to be 
endowed with movement, it would not lie alwaj^s at this 
point, it must, therefore, shift to some other part of the 
sphere. The movements of the stars, however, preclude 
the possibility of this ; and, therefore, the earth must be 
as devoid of any movement of translation as it is devoid 
of rotation. Thus it was that Ptolemy convinced himself 
that the stability of the earth, as it appeared to the ordi- 
nary senses, had a rational philosophical foundation. 

Not unfrequently it is the lot of the philosophers to 
contend against the doctrines of the vulgar, but when it 
happens, as in the case of Ptolemy's researches, that the 
doctrines of the vulgar are corroborated by philosophical 
investigation which bear the stamp of the highest 
authority, it is not to be wondered at that such doctrines 
should be deemed well-nigh impregnable. In this way we 
may, perhaps, account for the remarkable fact that the 
theories of Ptolemy held unchallenged sway over the 
human intellect for the vast period already mentioned. 

Up to the present we have been speaking only of those 
primary motions of the heavens, by which the whole 
sphere appeared to revolve once every twenty-four hours. 
We have now to discuss the remarkable theories by which 
Ptolemy endeavoured to account for the monthly move- 
ment of the moon, for the annual movement of the sun, 
and for the periodic movements of the planets which had 
gained for them the titles of the wandering stars. 

Possessed with the idea that these movements must 
be circular, or must be capable, directly or indirectly, of 
being explained by circular movements, it seemed obvious 
to Ptolemy, as indeed it had done to previous astronomers, 


that the track of the moon throusrh the stars was a circle 
of which the earth is the centre. A similar movement 
with a yearly period must also be attributed to the sun, 
for the changes in the positions of the constellations, in 
accordance with the progress of the seasons, placed it 
beyond doubt that the sun made a circuit of the celestial 
sphere, even though the bright light of the sun pre- 
vented the stars in its vicinity from being seen in day- 
light. Thus the movements both of the sun and the 
moon, as well as the diurnal rotation of the celestial 
sphere, seemed to justify the notion that all celestial 
movements must be " perfect," that is to say, described 
uniformly in those circles which were the only perfect 

The simplest observations, however, show that the 
movements of the planets cannot be explained in this 
simple fashion. Here the geometrical genius of Ptolemy 
shone forth, and he devised a scheme by which the appa- 
rent wanderings of the planets could be accounted for 
without the introduction of aught save *' perfect" move- 

To understand his reasoning, let us first set forth 
clearly those facts of observation which require to be 
explained. I shall take, in particular, two planets, Venus 
and Mars, as these illustrate, in the most striking manner, 
the peculiarities of the inner and the outer planets respec- 
tively. The simplest observations would show that Venus 
did not move round the heavens in the same fashion as 
the sun or the moon. Look at the evening star when 
brightest, as it appears in the west after sunset. Instead 
of moving towards the east among the stars, like the sun 


or the moon, we find, week after week, tkat Venus is 
drawing in towards the sun, until it is lost in the sun- 
beams. Then the planet emerges on the other side, not 
to be seen as an. evening star, but as a morning star. In. 
fact, it was plain that in some ways Yenus accompanied 
the sun in its annual movement. Now it is found advanc- 
ing in front of the sun to a certain limited distance, and 
now it is lagging to an equal extent behind the sun. 

,t-- ■■-... , 





FIG. I. 

These movements were wholly incompatible with the sup- 
position that the journeys of Yenus were described by a 
single motion of the kind regarded as perfect. It was 
obvious that the movement was connected in some strange 
manner with the revolution of the sun, and here was the in- 
genious method by which Ptolemy sought to render account 
of it. Imagine a fixed arm to extend from the earth to 
the sun, as shown in the accompanying figure (Fig. ]), 


then this arm will move round uniformly, in consequence 
of the sun's movement. At a point p on this arm let a 
small circle be described. Yenus is supposed to revolve 
uniformly in this small circle, while the circle itself is 
carried round continuously by the movement of the sun. 
In this way it was possible to account for the chief pecu- 
liarities in the movement of Yenus. It will be seen that, 
in consequence of the revolution around p, the spectator 
on the earth will sometimes see Yenus on one side of the 
sun, and sometimes on the other side, so that the planet 
always remains in the sun's vicinity. By properly pro- 
portioning the movements, this little contrivance simulated 
the transitions from the morning star to the evening star. 
Thus the changes of Yenus could be accounted for by a 
combination of the " perfect" movement of p in the circle 
which it described uniformly round the earth, combined 
with the *' perfect" motion of Yenus in the circle which 
it described uniformly around the moving centre. 

In a precisely similar manner Ptolemy rendered an 
explanation of the fitful apparitions of Mercury. Now 
just on one side of the sun, and now just on the other, 
this rarely-seen planet moved like Yenus on a circle 
whereof the centre was also carried by the line joining 
the sun and the earth. The circle, however, in which 
Mercury actually revolved had to be smaller than that of 
Yenus, in order to account for the fact that Mercury lies 
always much closer to the sun than the better-known 

The explanation of the movement of an outer planet 
like Mars could also be deduced from the joint effect of two 
perfect motions. The changes through which Mars goes 


••a MARS 

M ti'.-- 




TJG 2 

are, however, so different from the movements of Yenus 
that quite a different disposition of the circles is necessary. 
For consider the facts which characterise the movements 
of an outer planet such as Mars. In the first place. Mars 
accomplishes an entire circuit of the heaven. In this 
respect, no doubt, it may be said to resemble the sun or 
the moon. A little attention will, however, show that 
there are extraordinary irregularities in the movement of 
the planet. Generally speaking, it speeds its way from 
west to east among the stars, but sometimes the attentive 
observer will note that the speed with which the planet 
advances is slackening, and then it will seem to become 
stationary. Some days later the direction of the planet's 
movement will be reversed, and it will be found moving 
from the east towards the west. At first it proceeds 


slowly, and then quickens its pace, until a certain speed is 
attained, which afterwards declines until a second sta- 
tionary position is reached. After a due pause the original 
motion from west to east is resumed, and is continued 
until a similar cycle of changes again commences. Such 
movements as these were obviously quite at variance wdth 
any perfect movement in a single circle round the earth. 
Here, again, the geometrical sagacity of Ptolemy provided 
him with the means of representing the apparent move- 
ments of Mars, and, at the same time, restricting the 
explanation to those perfect movements which he deemed 
so essential. In Fig. 2 we exhibit Ptolemy's theory as to 
the movement of Mars. We have, as before, the earth at 
the centre, and the sun describing its circular orbit around 
that centre. The path of Mars is to be taken as exterior 
to that of the sun. We are to suppose that at a point 
marked m there is a fictitious planet, which revolves 
around the earth uniformly, in a circle called the deferent. 
This point m, which is thus animated by a perfect move- 
ment, is the centre of a circle which is carried onwards 
with M, and around the circumference of which Mars 
revolves uniformly. It is easy to show that the combined 
effect of these two perfect movements is to produce exactly 
that displacement of Mars in the heavens which observa- 
tion discloses. In the position represented in the figure, 
Mars is obviously pursuing a course which will appear to 
the observer as a movement from west to east. When, how- 
ever, the planet gets round to such a position as R, it is 
then moving from east to west in consequence of its revo- 
lution in the moving circle, as indicated by the arrow- 
head. On the other hand, the whole circle is carried 


forward in the opposite direction. If the latter move- 
ment be less rapid than the former, then we shall have 
the backward movement of Mars on the heavens which it 
was desired to explain. By a proper adjustment of the 
relative lengths of these arms the movements of the 
planet as actually observed could be completely accounted 

The other outer planets with which Ptolemy was ac- 
quainted, namely, Jupiter and Saturn, had movements of 
the same general character as those of Mars. Ptolemy 
was equally successful in explaining the movements 
they performed by the , supposition that each planet had 
perfect rotation in a circle of its own, which circle 
itself had perfect movement around the earth in the 

It is somewhat strange that Ptolemy did not advance 
one step further, as by so doing he would have given 
great simplicity to his system. He might, for instance, 
have represented the movements of Yenus equally well by 
putting the centre of the moving circle at the sun itself, 
and correspondingly enlarging the circle in which Yenus 
revolved. He might, too, have arranged that the several 
circles which the outer planets traversed should also have 
had their centres at the sun. The planetary system would 
then have consisted of an earth fixed at the centre, of a sun 
revolving uniformly around it, and of a system of planets 
each describing its own circle around a moving centre 
placed in the sun. Perhaps Ptolemy had not thought of 
this, or perhaps he may have seen arguments against it. 
This important step was, however, taken by Tycho. He 
considered that all the planets revolved around the sun in 


circles, and that the sun itself, bearing all these orbits, 
described a mighty circle around the earth. This point 
having been reached, only one more step would have been 
necessary to reach the glorious truths that revealed the 
structure of the solar system. That last step was taken 
by Co|; amicus. 


The quaint town of Thorn, on the Vistula, was more than 
two centuries old when Copernicus was born there on the 
19th of February, 1473. The situation of this town on 
the frontier between Prussia and Poland, with the com- 
modious waterway offered by the river, made it a place 
of considerable trade. A view of the town, as it was at 
the time of the birth of Copernicus, is here given. The 
walls, with their watch-towers, will be noted, and the 
strategic importance which the situation of Thorn gave 
to it in the fifteenth century still belongs thereto, so 
much so that the German Government recently consti- 
tuted the town a fortress of the first class. 

Copernicus, the astronomer, whose discoveries make 
him the great predecessor of Kepler and IN'ewton, did not 
come from a noble family, as certain other early astro- 
nomers have done, for his father was a tradesman. 
Chroniclers are, however, careful to tell us that one of 
his uncles was a bishop. We are not acquainted with 
any of those details of his childhood or youth which are 
often of such interest in other cases where men have risen 
to exalted fame. It would appear that the young Nico- 
laus, for such was his Christian name, received his educa- 


tion at home uutil such time as lie was deemed sufficiently 
advanced to be sent to the University at Cracow. The 
education that he 
there obtained must 
have been in those 
days of a very primi- 
tive description, but 
Copernicus seems to 
have availed himself 
of it to the utmost. 
He devoted himself 
more particularly to 
the study of medi- 
cine, with the view 
of adopting its prac- 
tice as the profession 
of his life. The ten- 
dencies of the future 
astronomer were, 
however, revealed in 
the fact that he 
worked hard at ma- 
thematics, and, like 
one of his illustrious 
successors, Galileo, 
the practice of the 
art of painting had 
for him a very great 
interest, and in it he obtained some measure of success. 

By the time he was twenty -seven years old, it would 
seem that Copernicus had given up the notion of becoming 


a medical practitioner, and had resolved to devote him- 
self to science. He was engaged in teaching mathe- 
matics, and appears to have acquired some reputation. 
His growing fame attracted the notice of his uncle the 
bishop, at whose suggestion Copernicus took holy orders, 
and he was presently appointed to a canonry in the 
cathedral of Frauenburg, near the mouth of the Vistula. 

To Frauenburg, accordingly, this man of varied gifts 
retired. Possessing somewhat of the ascetic spirit, he 
resolved to devote his life to work of the most serious 
description. He eschewed all ordinary society, restrict- 
ing his intimacies to very grave and learned companions, 
and refusing to engage in conversation of any useless 
kind. It would seem as if his gifts for painting were 
condemned as frivolous; at all events, we do not learn 
that he continued to practise them. In addition to the 
discharge of his theological duties, his life was occupied 
partly in ministering medically to the wants of the poor, 
and partly with his researches in astronomy and mathe- 
matics. His equipment in the matter of instruments for 
the study of the heavens seems to have been of a very 
meagre description. He arranged apertures in the walls 
of his house at Allenstein, so that he could observe in 
some fashion the passage of the stars across the meridian. 
That he possessed some talent for practical mechanics is 
proved by his construction of a contrivance for raising 
water from a stream, for the use of the inhabitants of 
Frauenburg. Relics of this machine are still to be 

The intellectual slumber of the Middle Ages was des- 
tined to be awakened by the revolutionary doctrines of 




Copernicus. It may be noted, as an interesting circum- 
stance, that tlie time at which he discovered the scheme of 
the solar system has coincided with a remarkable epoch in 
the world's history. The great astronomer had just reached 
manhood at the time when Columbus discovered the new 

Before the publication of the researches of Copernicus, 
the orthodox scientific creed averred that the earth was 
stationary, and that the apparent movements of the 



heavenly bodies were indeed real movements. Ptolemy 
had laid down this doctrine 1,400 years before. In his 
theory this huge error was associated with so much im- 
portant truth, and the whole presented such a coherent 
scheme for the explanation of the heavenly movements, 
that the Ptolemaic theory was not seriously questioned 
until the great work of Copernicus appeared. No doubt 
others, before Copernicus, had from time to time in some 
vague fashion surmised, with more or less plausibility, 
that the sun, and not the earth, was . the centre about 
which the system really revolved. It is, however, one 
thing to state a scientific fact ; it is quite another thing 
to be in possession of the train of reasoning, founded on 
observation or experiment, by which that fact may be 
established. Pythagoras, it appears, had indeed told his 
disciples that it was the sun, and not the earth, which 
was the centre of movement, but it does not seem at all 
certain that Pythagoras had any grounds which science 
could recognise for the belief which is attributed to him. 
So far as information is available to us, it would seem 
that Pythagoras associated his scheme of things celestial 
with a number of preposterous notions in natural philo- 
sophy. He may certainly have made a correct statement 
as to which was the most important body in the solar 
system, but he certainly did not provide any rational 
demonstration of the fact. Copernicus, by a strict train 
of reasoning, convinced those who would listen to him 
that the sun was the centre of the system. It is useful 
for us to consider the arguments which he urged, and by 
which he effected that intellectual revolution which is 
always connected with his name. 


The first of the great discoveries which Copernicus made 
relates to the rotation of the earth on its axis. That 
general diurnal movement, by which tlie stars and all other 
celestial bodies appear to be carried completely round the 
heavens once every twenty-four hours, had been accounted 
for by Ptolemy on the supposition that the apparent 
movements were the real movements. As we bave already 
seen, Ptolemy himself felt the extraordinary difficulty 
involved in the supposition that so stupendous a fabric 
as the celestial sphere should spin in the way supposed. 
{Such movements required that many of the stars should 
travel with almost inconceivable velocity. Copernicus also 
saw that the daily rising and setting of the heavenly 
bodies could be accounted for either by the suj^position 
that the celestial sphere moved round and that the earth 
remained at rest, or by the supposition that the celestial 
sphere was at rest while the earth turned round in the oppo- 
site direction. He weighed the arguments on both sides 
as Ptolemy had done, and, as the result of his delibera- 
tions, Copernicus came to an opposite conclusion from 
Ptolemy. To Copernicus it appeared that the difficulties 
attending the supposition that the celestial sphere re- 
volved, were vastly greater than those which appeared 
so weighty to Ptolemy as to force him to deny the earth's 

Copernicus shows clearly how the observed phenomena 
could be accounted for j ust as completely by a rotation of 
the earth as by a rotation of the heavens. He alludes to 
the fact that, to those on board a vessel which is moving 
through smooth water, the vessel itself appears to be at 
rest, while the objects on shore seem to be moving past. 


If, therefore, tlie eartli were rotating tiniformly, we 
dwellers upon the eartli, oblivious of our own move- 
ment, would wrongly attribute to the stars the dis- 
placement which was actually the consequence of our own 

Copernicus saw the futility of the arguments by which 
Ptolemy had endeavoured to demonstrate that a revolu- 
tion of the earth was impossible. It was plain to him 
that there was nothing whatever to warrant refusal to 
believe in the rotation of the earth. In his clear-sighted- 
ness on this matter we have specially to admire the saga- 
city of Copernicus as a natural philosopher. It had been 
urged that, if the earth moved round, its motion would 
not be imparted to the air, and that therefore the earth 
would be uninhabitable by the terrific winds which would 
be the result of our being carried through the air. Coj)er- 
nicus convinced himself that this deduction was prepos- 
terous. He proved that the air must accompany the 
earth, just as his coat remains round him, notwithstand- 
ing the fact that he is walking down the street. In this 
way he was able to show that all a priori objections to the 
earth's movements were absurd, and therefore he was able 
to compare together the plausibilities of the two rival 
schemes for explaining the diurnal movement. 

Once the issue had been j)laced in this form, the result 
could not be long in doubt. Here is the question : Which 
is it more likely — that the earth, like a grain of sand at 
the centre of a mighty globe, should turn round once in 
twenty-four hours, or — that the whole of that vast globe 
should complete a rotation in the opposite direction in the 
same time ? Obviously, the former is far the more simple 



supposition. But the case is really much stronger than 
this. Ptolemy had supposed that all the stars were attached 





He had no ground whatever 

to the surface of a sphere. 

for this supposition, except that otherwise it would have 

been well-nigh impossible to have devised a scheme by 


whicli the rotation of the heavens around a fixed earth 
could have been arranged. Copernicus, however, with 
the just instinct of a philosopher, considered that the 
celestial sphere, however convenient from a geometrical 
point of view, as a means of representing apparent pheno- 
mena, could not actually have a material existence. In 
the first place, the existence of a material celestial sphere 
would require that all the myriad stars should be at 
exactly the same distances from the earth. Of course, 
no one will say that this or any other arbitrary disposi- 
tion of the stars is actually impossible, but as there was no 
conceivable physical reason why the distances of all the 
stars from the earth should be identical, it seemed in the 
very highest degree improbable that the stars should be 
so placed. 

Doubtless, also, Copernicus felt a considerable difficulty 
as to the nature of the materials from which Ptolemy's 
wonderful sphere was to be constructed. J^or could a 
philosopher of his penetration have failed to observe that, 
unless that sphere were infinitely large, there must have 
been space outside it, a consideration which would open up 
other difficult questions. Whether infinite or not, it was 
obvious that the celestial sphere must have a diameter 
at least many thousands of times as great as that of 
the earth. From these considerations Copernicus deduced 
the important fact that the stars and the other celestial 
bodies must all be vast objects. He was thus enabled to 
put the question in such a form that it could hardly 
receive any answer but the correct one. Which is it 
more rational to suppose, that the earth should turn round 
on its axis once in twenty-four hours, or that thousands of 


mighty stars should circle round the earth in the same 
time, many of them having to describe circles many 
thousands of times greater in circumference than the 
circuit of the earth at the equator ? The obvious answer 
pressed upon Copernicus with so much force that he was 
compelled to reject Ptolemy's theory of the stationary 
earth, and to attribute the diurnal rotation of the heavens 
to the revolution of the earth on its axis. 

Once this tremendous step had been taken, the great 
difficulties which beset the monstrous conception of the 
celestial sphere vanished, for the stars need no longer 
be regarded as situated at equal distances from the 
earth. Copernicus saw that they might lie at the most 
varied degrees of remoteness, some being hundreds or 
thousands of times farther away than others. The com- 
plicated structure of the celestial sphere as a material 
object disappeared altogether ; it remained only as a 
geometrical conception, whereon we find it convenient to 
indicate the places of the stars. Once the Copernican 
doctrine had been fully set forth, it was impossible for 
anyone, who had both the inclination and the capacity to 
understand it, to withhold acceptance of its truth. The 
doctrine of a stationary earth had gone for ever. 

Copernicus having established a theory of the celestial 
movements which deliberately set aside the stability of the 
earth, it seemed natural that he should inquire whether 
the doctrine of a moving earth might not remove the 
difficulties presented in other celestial phenomena. It 
had been universally admitted that the earth lay un- 
supported in space. Copernicus had further shown that 
it possessed a movement of rotation. Its want of stability 


being thus recognised, it seemed reasonable to suppose 
that the earth might also have some other kinds of move- 
ments as well. In this, Copernicus essayed to solve a 
problem far more difficult than that which had hitherto 
occupied his attention. It was a comparatively easy task 
to show how the diurnal rising and setting could be 
accounted for by the rotation of the earth. It was a 
much more difficult undertaking to demonstrate that the 
planetary movements, which Ptolemy had represented 
with so much success, could be completely explained by 
the supposition that each of those planets revolved uni- 
formly round the sun, and that the earth was also a 
planet, accomplishing a complete circuit of the sun once 
in the course of a year. 

It would be impossible in a sketch like the present to 
enter into any detail as to the geometrical propositions on 
which this beautiful investigation of Copernicus depended. 
We can only mention a few of the leading principles. 
It may be laid down in general that, if an observer is in 
movement, he will, if unconscious of the fact, attribute to 
the iixed objects around him a movement equal and oppo- 
site to that which he actually possesses. A passenger on 
a canal-boat sees the objects on the banks apparently 
moving backward with a speed equal to that by which he 
is himself advancing forwards. By an application of this 
principle, we can account for all the phenomena of the 
movements of the planets, which Ptolemy had so in- 
geniously represented by his circles. Let us take, for 
instance, the most characteristic feature in the irregu- 
larities of the outer plane ta. We have already remarked 
that Mars, though generally advancing from west to east 


among the stars, occasionally pauses, retraces Ms steps for 
a while, again pauses, and then resumes his ordinary 
onward progress. Copernicus showed clearly how this 
effect was produced by the real motion of the earth, com- 
bined with the real motion of Mars. In the adjoining 
figure we represent a portion of the circular tracks 
in which the earth and Mars move in accordance with 




the Copernican doctrine. I show particularly the case 
where the earth comes directly between the planet and 
the sun, because it is on such occasions that the retro- 
grade movement (for so this backward movement of Mars 
is termed) is at its highest. Mars is then advancing in 
the direction shown by the arrow-head, and the earth is 
also advancing in the same direction. We, on the earth, 
however, being unconscious of our owm motion, attribute, 


by tlie principle I liave already explained, an equal and 
opposite motion to Mars. The visible effect upon the 
planet is, that Mars bas two movements, a real onward 
movement in one direction, and an apparent movement in 
the opposite direction. If it so happened that the earth 
was moving with the same speed as Mars, then the 
apparent movement would exactly neutralise the real 
movement, and Mars would seem to be at rest relatively 
to the surrounding stars. Under the actual circumstances 
represented, however, the earth is moving faster than 
Mars, and the consequence is, that the apparent move- 
ment of the planet backwards exceeds the real movement 
forwards, the net result being an apparent retrograde 

With consummate skill, Copernicus showed how the 
applications of the same principles could account for the 
characteristic movements of the planets. His reasoning 
in due time bore down all opposition. The supreme im- 
portance of the earth in the system vanished. It had 
now merely to take rank as one of the planets. 

The same great astronomer now, for the first time, 
rendered something like a rational account of the changes 
of the seasons. Nor did certain of the more obscure 
astronomical phenomena escape his attention. 

He delayed publishing his wonderful discoveries to the 
world until he was quite an old man. He had a well- 
founded apprehension of the storm of opposition which 
they would arouse. However, he yielded at last to the 
entreaties of his friends, and his book was sent to the 
press. But ere it made its appearance to the world, 
Copernicus was seized by mortal illness. A copy of the 


book was brought to him on May 23, 1543. We are 
told tbat be was able to see it and to touch it, but 
no more, and he died a few hours afterwards. He was 
buried in that Cathedral of Frauenburg, with which his 
life had been so closely associated. 


The most picturesque figure in the history of astronomy 
is undoubtedly that of the famous old Danish astronomer 
whose name stands at the head of this chapter. Tycho 
Brahe was alike notable for his astronomical genius and 
for the extraordinary vehemence of a character which 
was by no means perfect. His romantic career as a philo- 
sopher, and his taste for splendour as a Danish noble, his 
ardent friendships and his furious quarrels, make him an 
ideal subject for a biographer, while the magnificent 
astronomical work which he accomplished has given him 
imperishable fame. 

The history of Tycho Brahe has been admirably told by 
Dr. Dreyer, the accomplished astronomer who now directs 
the observatory at Armagh, though himself a countryman 
of Tycho. Every student of the career of the great Dane 
must necessarily look on Dr. Dreyer's work as the chief 
authority on the subject. Tycho sprang from an illustrious 
stock. His family had flourished for centuries, both in 
Sweden and in Denmark, where his descendants are to be 
met with at the present day. The astronomer's father 
was a privy councillor, and having filled important posi- 
tions in the Danish government, he was ultimately pro- 
moted to be governor of Helsingborg Castle, where he 


spent the last years of his life. His illustrious son Tycho 
was born in 1546, and was the second child and eldest 
boy in a family of ten. 

It appears that Otto, the father of Tycho, had a brother 
named George, who was childless. George, howeyer, 
desired to adopt a boy on whom he could lavish his affec- 
tion and to whom he could bequeath his wealth. A some- 
what singular arrangement was accordingly entered into 
by the brothers at the time when Otto was married. It 
was agreed that the first son who might be born to Otto 
should be forthwith handed over by the parents to George 
to be reared and adopted by him. In due time little 
Tycho appeared, and was immediately claimed by George 
in pursuance of the compact. But it was not unnatural 
that the parental instinct, which had been dormant when 
the agreement was made, should here interpose. Tj^cho's 
father and mother receded from the bargain, and refused 
to part with their son. George thought he was badly 
treated. However, he took no violent steps until a year 
later, when a brother was born to Tycho. The uncle then 
felt no scruple in asserting what he believed to be his 
rights by the simple process of stealing the first-born 
nephew, which the original bargain had promised him. 
After a little time it would seem that the parents acquiesced 
in the loss, and thus it was in Uncle George's home that 
the future astronomer passed his childhood. 

When we read that Tycho was no more than thirteen 
years old at the time he entered the University of Copen- 
hagen, it might be at first supposed that even in his boyish 
years he must have exhibited some of those remarkable 
talents with which he was afterwards to astonish the 


world. Such an inference should not, however, be drawn. 
The fact is that in those days it was customary for students 
to enter the universities at a much earlier age than is now 
the case. Not, indeed, that the boys of thirteen knew more 
then than the boys of thirteen know now. But the edu- 
cation imparted in the universities at that time was of a 
much more rudimentary kind than that which we under- 
stand by university education at present. In illustration 
of this Dr. Dreyer tells us how, in the University of 
Wittenberg, one of the professors, in his opening address, 
was accustomed to point out that even the processes of 
multiplication and division in arithmetic might be learned 
by any student who possessed the necessary diligence. 

It was the wish and the intention of his uncle that Tycho's 
education should be specially directed to those branches 
of rhetoric and philosophy which were then supposed to 
be a necessary preparation for the career of a statesman. 
Tycho, however, speedily made it plain to his teachers 
that though he was an ardent student, yet the things 
which interested him were the movements of the heavenly 
bodies and not the subtleties of metaphysics. 

On the 21st October, 1560, an eclipse of the sun 
occurred, which was partially visible at Copenhagen. 
Tycho, boy though he was, took the utmost interest in 
this event. His ardour and astonishment in connection 
with the circumstance were chiefly excited by the fact that 
the time of the occurrence of the phenomenon could be 
predicted with so much accuracy. Urged by his desire to 
understand the matter thoroughly, Tycho sought to pro- 
cure some book which might explain what he so greatly 
wanted to know. In those days books of any kind were 


Tycho Brah.e. 

but few and scarce, and scientific books were especially 
unattainable. It so happened, however, that a Latin 
version of Ptolemy^s astronomical works had appeared a 
few years before the eclipse took place, and T3xho managed 
to buy a copy of this book, Vv^hich was then the chief 


authority on celestial matters. Young as the boy astro- 
nomer was, lie studied hard, although perhaps not always 
successfully, to understand. Ptolemy, and to this day his 
copy of the great work, copiously annotated and marked 
by the schoolboy hand, is preserved as one of the chief 
treasures in the library of the University at Prague. 

After Tycho had studied for about three years at the 
University of Copenhagen, his uncle thought it would be 
better to send him, as was usual in those days, to com- 
plete his education by a course of study in some foreign 
university. The uncle cherished the hope that in this 
way the attention of the young astronomer might be 
withdrawn from the study of the stars and directed in 
what appeared to him a more useful way. Indeed, to the 
wise heads of those days, the pursuit of natural science 
seemed "so much waste of good time which might other- 
wise be devoted to logic or rhetoric or some other .branch 
of study more in vogue at that time. To assist in this 
attempt to wean Tycho from his scientific tastes, his uncle 
chose as a tutor to accompany him an intelligent and 
upright young man named Yedel, who was four years 
senior to*his pupil, and accordingly, in 1562, we find the 
pair taking up their abode at the University of Leipzig. 

The tutor, however, soon found that he had undertaken 
a most hopeless task. He could not succeed in imbuing 
Tycho with the slightest taste for the study of the law or 
the other branches of knowledge which were then thought 
so desirable. The stars, and nothing but the stars, en- 
oTossed the attention of his pupil. We are told that all 
the money he could obtain was spent secretly in buying 
astronomical books and instruments. He learned the 


name of the stars from a little globe, wliicli lie kept hidden 
from Yedel, and only ventured to use during the latter's 
absence. JS'o little friction was at first caused by all this, 
but in after years a fast and enduring friendship grew up 
between Tycho and his tutor, each of whom learned to 
respect and to love the other. 

Before Tycho was seventeen he had commenced the 
difficult task of calculating the movements of the planets 
and the places which they occupied on the sky from time 
to time. He was not a little surprised to find that the 
actual positions of the planets differed very widely from 
those which were assigned to them by calculations from 
the best existing works of astronomers. With the insio-ht 
of genius he saw that the only true method of investiga- 
ting the movements of the heavenly bodies would be to 
carry on a protracted series of measurements of their 
places. This, which now seems to us so obvious, was then 
an entirely new doctrine. Tycho at once commenced 
regular observations in such fashion as he could. His 
first instrument was, indeed, a very primitive one, consist- 
ing of a simple pair of compasses, which he used in this 
wa}^ He placed his eye at the hinge, and then opened 
the legs of the compass so that one leg pointed to one 
star and the other leg to the other star. The compass 
was then brought down to a divided circle, by which 
means the number of degrees in the apparent angular dis- 
tance of the two stars was determined. 

His next advance in instrumental equipment was to 
provide himself with the contrivance known as the '^ cross- 
staff," with which he used to observe the stars whenever 
opportunity offered. It must, of course, be remembered 




that in those daj^s there were no telescopes. In the 
absence of optical aid, such as lenses afford the modern 
observers, astronomers had to rely on mechanical ap- 
pliances alone to measure the places of the stars. Of 
such appliances, perhaps the most ingenious was one 
known before Tycho's time, which we have represented 
in the adjoining figure. 

Let us suppose that it be desired to measure the angle 


TO .STAp_ 




e J3 


between two stars, then if the angle be not too large it 
can be determined in the following manner. Let the rod 
A B be divided into inches and parts of an inch, and let 
another rod, c d, slide up and down along a b in such a 
way that the two always remain perpendicular to each 
other. " Sights,'* like those on a rifle, are placed at a 
and c, and there is a pin at d. It will easily be seen that, 
by sliding the movable bar along the fixed one, it must 
always be possible when the stars are not tPQ far apart tQ 



bring the sights into such positions that one star can be 
seen along d c and the other along d a. This having been 
accomplished, the length from a to the cross-bar is read 
off on the scale, and then, by means of a table previouslj^ 
prepared, the value of the required angular distance is 
obtained. If the angle between the two stars were 
greater than it would be possible to measure in the way 
already described, then there was a provision by which 
the pin at d might be moved along c d into some other 
position, so as to bring the angular distance of the stars 
within the range of the instrument. 

No doubt the cross- staff is a very primitive contrivance, 
but when handled by 
one so skilful as Tycho 
it afforded results of 
considerable accuracy. 
I would recommend 
any reader who may 
have a taste for such 
pursuits to construct 
a cross- staff for him- 
self, and see what mea- 
surements he can ac- 
complish with its aid. 

To employ this little 
instrument Tycho had 
to evade the vigilance 
of his conscientious 
tutor, who felt it his 
duty to interdict all 

^ . Tycho's " New Star " Sextant of 1572. 

PUCh OCCUpatlOllS as ^Tj^g^yp^p^of^aluut-wooa, are about 6f ft. long. 



being a frivolous waste 
of time. It was when 
Yedel was asleep tliat 
Tycho managed to 
escape with his cross - 
staff and measure the 
places of the heavenly- 
bodies. Even at this 
early age Tycho used 
to conduct his obser- 
vations on those tho- 
roughly sound prin- 
ciples which lie at the 
foundation of all ac- 
curate modern astro- 
nomy. Recognising 
the inevitable errors 
of workmanship in his 
little instrument, he 
ascertained their 
amount and allowed for their influence on the results 
which he deduced. This principle, employed by the boy 
with his cross-staff in 1564, is employed at the present 
day by the Astronomer E,oyal at Greenwich with the 
most superb instruments that the skill of modern opticians 
has been able to construct. 

After the death of his uncle, when Tycho was nineteen 
years of age, it appears that the young philosopher was 
no longer interfered with in so far as the line which his 
studies were to take was concerned. Always of a some- 
what restless temperament, we now find that he shifted 

Tycho' s TrigOBic Sextant. 
(The arms, AB and A C, are about 5J ft. long.) 



his abode to tlie University of Rostock, where he speedily 
made himself notable in connection with an eclipse of 
the moon on 28th October, 1566. Like every other 
astronomer of those days, Tycho had always associated 
astronomy with astrology. He considered that the 
phenomena of the heavenly bodies always had some 
significance in connection with human affairs. Tycho was 
also a poet, and in the united capacity of poet, astrologer, 
and astronomer, he posted up some verses in the college 
at Rostock announcing that the lunar eclipse was a prog- 
nostication of the death of the great Turkish Sultan, 
whose mighty deeds 
at that time filled 
men's minds. Pre- 
sently news did 
arrive of the death 
of the Sultan, and 
Tycho was accord- 
ingly triumphant ; 
but a little later it 
appeared that the de- 
cease had taken place 
before the eclipse, a 
circumstance which 
caused many a laugh 
at Tycho's expense. 

Tvcho beinff of a 
somewhat turbulent 
disposition, it appears 
that, while at the Uni- 

Tycho' s Astronomic Sextant. 
VerSlty of Rostock, (Madeofeteel; thearms,^5,^C,measure4ft.) 



lie had a serious 
quarrel with, another 
Danish nobleman. "We 
are not told for cer- 
tain what was the 
cause of the dispute. 
It does not, however, 
seem to have had any 
more romantic origin 
than a difference of 
opinion as to which 
of them knew the more 
mathematics. They 
fought, as perhaps it 
was becoming for two 
astronomers to fight, 
under the canopy of 
heaven in utter dark- 
ness, at the dead of 
night, and the duel 
was honourably ter- 
minated when a slice was taken off Tycho's nose by the 
insinuating sword of his antagonist. For the repair of 
this injury the ingenuity of the great instrument-maker 
was here again useful, and he made a substitute for his 
nose "with a composition of gold and silver." The 
imitation was so good that it is declared to have been 
quite equal to the original. Dr. Lodge, however, 
pointedly observes that it does not appear whether this 
remark was made by a friend or an enemy. 

The next few years Tycho spent in various places 









i 1 






W^^^^^^^y^^ A 















"^^^z ^^" 

Tycho's Equatorial ArmiUary. 

(The meridian circle, E B A D, made of solid 
steel, is nearly 6 ft. in diameter.) 



ardently pursuing somewliat varied branches of scientific 
study. At one time we hear of him assisting an astro- 
nomical alderman, in the ancient city of Augsburg, to 
erect a tremendous wooden machine — a quadrant of 
19-feet radius — to be used in observing the heavens. 
At another time we learn that the King of Denmark had 
recognised the talents of his illustrious subject, and 
promised to confer on him a pleasant sinecure in the shape 
of a canonry, which would assist him with the means for 
indulging his scientific pursuits. Again we are told that 
Tj^cho is pursuing experiments in chemistry with the 
greatest energy, nor 
is this so incompa- 
tible as might at 
first be thought with 
his devotion to astro- 
nomy. In those early 
days of knowledge 
the different sciences 
seemed bound to- 
gether by mysterious 
bonds. Alchemists 
and astrologers 
taught that the 
several planets were 
correlated in some 
mysterious manner 
with the several 
metals. It was, there- 

' J P ' rpj^g ^g^^ Augsburg Quadrant, 

ing that Tycho (Built of heart of oak; the radii about 19 ft.] 



Tycho's "New Scheme of tlie Terrestrial System," 1577. 

(should have included a study of the properties of the 
metals in the programme of his astronomical work. 

An event, however, occurred in 1572 which stimulated 
Tycho's astronomical labours, and started him on his life's 
work. On the 11th of November in that year, he was 
returning home to supper after a day's work in his 
laboratory, when he happened to lift his face to the sky, 
and there he beheld a brilliant new star. It was in the 
constellation of Cassiopeia, and occupied a position in 
which there had certainly been no bright star visible 
when his attention had last been directed to that part of 



the heavens. Such a phenomenon was so startling that 
he found it hard to trust the evidence of his senses. He 
thought he must be the subject of some hallucination. 
He therefore called to the servants who were accompany- 
ing him, and asked them whether they, too, could see a 
brilliant object in the direction in which he pointed. 
They certainly could, and thus he became convinced that 
this marvellous object was no mere creation of the fancy, 
but a veritable celestial body — a new star of surpassing 
splendour which had suddenly burst forth. In these days 
of careful scrutiny of the heavens, we are accustomed to 


Uraniborg and its grounds „ 





Ground-plan of the Observatory. 

the occasional outbreak of new stars. It is not, however, 
believed that any new star wbicb has ever appeared has 
displaj^ed the same phenomenal brilliance as was exhibited 
by the star of 1572. 

This object has a value in astronomy far greater than 
might at first appear. It is true, in one sense, that Tycho 
discovered the new star, but it is equally true, in a dif- 
ferent sense, that it was the new star which discovered 
Tycho. Had it not been for this opportune apparition, 
it is quite possible that Tycho might have found a career 
in some direction less beneficial to science than that which 
he ultimately pursued. 

When he reached his home on this memorable evening, 
Tycho immediately applied his great quadrant to the 
measurement of the place of the new star. His observa- 
tions were specially directed to the determination of the 
distance of the object. He rightly conjectured that if it 
were very much nearer to us than the stars in its vicinity, 



the distance of the brilliant body might be determined in 
a short time by the apparent changes in its distance from 
the surrounding points. It was speedily demonstrated 
that the new star could not be as near as the moon, by 
the simple fact that its apparent place, as compared with 
the stars in its neighbourhood, was not appreciably altered 
when it was observed below the pole, and again above 
the pole at an interval of twelve hours. Such observa- 
tions were possible, inasmuch as the star was bright 
enough to be seen in full daylight. Tycho thus showed 
conclusively that the body was so remote that the diameter 
of the earth bore an insignificant ratio to the star's dis- 
tance. His success in this respect is the more noteworthy 
when we find that many other observers, who studied the 
same object, came to the erroneous conclusion that the 
new star was quite as near as the moon, or even much 

The Observatory of Uraniborg, Island of Hven. 


nearer. In fact, it may be said, that with regard to this 
object Tycho discovered everything which could possibly 
have been discovered in the days before telescopes were 
invented. He not only proved that the star's distance 
was too great for measurement, but he showed that it 
had no proper motion on the heavens. He recorded the 
successive changes in its brightness from week to week, 
as well as the fluctuations in hue with which the altera- 
tions in lustre were accompanied. 

It seems, nowadays, strange to find that such tho- 
roughly scientific observations of the new star as those 
which Tycho made, possessed, even in the eyes of the 
great astronomer himself, a profound astrological signi- 
ficance. We learn from Dr. Dreyer that, in Tycho' s opinion, 
"the star was at first like Yenus and Jupiter, and its 
efi'ects will therefore, first, be pleasant ; but as it then 
became like Mars, there will next come a period of wars, 
seditions, captivity, and death of princes, and destruction 
of cities, together with dryness and fiery meteors in the 
air, pestilence, and venomous snakes. Lastly, the star 
became like Saturn, and thus will finally come a time of 
want, death, imprisonment, and all kinds of sad things ! " 
Ideas of this kind were, however, universally entertained. 
It seemed, indeed, obvious to learned men of that period 
that such an apparition must forebode startling events. 
One of the chief theories then held was, that just as the 
Star of Bethlehem announced the first coming of Christ, 
so the second coming, and the end of the world, was 
heralded by the new star of 1572. 

The researches of Tycho on this object were the occa- 
sion of his first appearance as an author. The publication 



of tiis book was, however, for some time delayed by tlie 
urgent remonstrances of his friends, who thought it was 
entirely beneath the dignity of a nobleman to condescend 
to write a book. Happily, Tycho determined to brave the 
opinion of his order ; the book appeared, and was the first 
of a series of great astronomical productions from the same 

The fame of the noble 
Dane being now widespread, 
the King of Denmark en- 
treated him to return to his 
native country, and to de- 
liver a course of lectures on 
astronomy in the Univer- 
sity of Copenhagen. With 
some reluctance he con- 
sented, and his introductory 
oration has been preserved. 
He dwells, in fervent lan- 
guage, upon the beauty and 
the interest of the celestial 

phenomena. He points out plL^^ 

the imperative necessity of 

Effigy on Tycho' s Tomb at Prague. 

continuous and systematic 
observation of the heavenly bodies in order to extend our 
knowledge. He appeals to the practical utility of the 
science, for what civilised nation could exist without hav- 
ing the means of measuring time ? He sets forth how the 
study of these beautiful objects ^'exalts the mind from 
earthly and trivial things to heavenly ones ;'* and then he 
winds up by assuring them that '^ a special use of astro- 


noray is that it enables us to draw conclusions from the 
movements in the celestial regions as to human fate." 

An interesting event, which occurred in 1572, distracted 
Tycho's attention from astronomical matters. He fell 
in love. The young girl on whom his affections were 
set appears to have sprung from humble origin. Here 
again his august family friends sought to dissuade him 
from a match they thought unsuitable for a nobleman. 
But Tycho never gave way in anything. It is sug- 
gested that he did not seek a wife among the high- 
born dames of his own rank from the dread that the 
demands of a fashionable lady would make too great an 
inroad on the time that he wished to devote to science. 
At all events, Tycho's union seems to have been a happy 
one, and he had a large family of childen ; none of whom, 
however, inherited their father's talents. 

Tycho had many scientific friends in Germany, among 
whom his work was held in high esteem. The treatment 
that he there met with seemed to him so much more 
encouraging than that which he received in Denmark that 
he formed the notion of emigrating to Basle and making 
it his permanent abode. A whisper of this intention was 
conveyed to the large-hearted King of Denmark, Frederick 
II. He wisely realised how great would be the fame 
which would accrue to his realm if he could induce Tycho 
to remain within Danish territory and carry on there the 
great work of his life. A resolution to make a splendid 
proposal to Tycho was immediately formed. A noble 
youth was forthwith despatched as a messenger, and 
ordered to travel day and night until he reached Tycho, 
whom he was to suinmon to the king. The astronomer 


Tycho's Mural Quadrant Picture, Uraniborg. 

was in bed on the morning of lltli February, 1576, when 
the message was delivered. Tycho, of course, set off at 
once, and had an audience of the king at Copenhagen. 
The astronomer explained that what he wanted was the 
means to pursue his studies unmolested, whereupon the 


king offered him the Island of Hven, in the Sound near 
Elsinore. There he would enjoy all the seclusion that he 
could desire. The king further promised that he would 
provide the funds necessary for building a house and for 
founding the greatest observatory that had ever yet been 
reared for the study of the heavens. After due delibera- 
tion and consultation with his friends, Tycho accepted the 
king's offer. He was forthwith granted a pension, and a 
deed was drawn up formally assigning the Island of Even 
to his use all the days of his life. 

The foundation of the famous castle of Uraniborg was 
laid on 30th August, 1576. The ceremony was a formal 
and imposing one, in accordance with Tycho's ideas of 
splendour. A party of scientific friends had assembled, 
and the time had been chosen so that the heavenly bodies 
were auspiciously placed. Libations of costly wines were 
poured forth, and the stone was placed with due solemnity. 
The picturesque character of this wonderful temple for the 
study of the stars may be seen in the figures with which 
this chapter is illustrated. 

One of the most remarkable instruments that has ever 
been employed in studying the heavens was the mural 
quadrant which Tycho erected in one of the apartments of 
Uraniborg. By its means the altitudes of the celestial 
bodies could be observed with much greater accuracy than 
had been previously attainable. This wonderful contriv- 
ance is represented on the preceding page. It will be 
observed that the walls of the room are adorned by 
pictures with a lavishness of decoration not usually to be 
found in scientific establishments. 

A few years later, when the fame of the observatory at 


Hven became more widely spread, a number of young men 
flocked to Tycbo to study under bis direction. He tbere- 
fore built anotber observatory for tbeir use in wbicb tbe 
instruments were placed in subterranean rooms of wbich 
only tbe roofs appeared above tbe ground. Tbere was a 
wonderful poetical inscription over tbe entrance to tbis 
underground observatory, expressing tbe astonisbment of 
Urania at finding, even in tbe interior of tbe eartb, a 
cavern devoted to tbe study of tbe beavens. Tycbo was 
indeed always fond of versifying, and be lost no oppor- 
tunity of indulging tbis taste wbenever an occasion pre- 
sented itself. 

Around tbe walls of tbe subterranean observatory were 
tbe pictures of eigbt astronomers, eacb witb a suitable 
inscription — one of tbese of course represented Tycbo 
bimself, and beneatb were written words to tbe effect tbat 
posterity sbould judge of bis work. Tbe eigbtb picture 
depicted an astronomer wbo bas not yet come into exists 
ence. Tycbonides was bis name, and tbe inscription 
expresses tbe modest bope tbat wben be does appear be 
will be wortby of bis great predecessor. Tbe vast 
expenses incurred in tbe erection and tbe maintenance of 
tbis strange establisbment were defrayed by a succession 
of grants from tbe royal purse. 

For twenty years Tycbo laboured bard at Uraniborg irt 
tbe pursuit of science. His work mainly consisted in tbe 
determination of tbe places of tbe moon, tbe planets, and 
tbe stars on tbe celestial spbere. Tbe extraordinary pains 
taken by Tycbo to bave bis observations as accurate as 
bis instruments would permit, bave justly entitled bim to 
tbe admiration of all succeeding astronomers. His island 



home provided the means of recreation as well as a place 
for work. He was surrounded by his family, troops of 
friends were not wanting, and a pet dwarf seems to have 
been an inmate of his curious residence. By way of 
change from his astronomical labours he used frequently 
to work with his students in his chemical laboratory. It 
is not indeed known what particular problems in chemistry 
occupied his attention. We are told, however, that he 
engaged largely in the production of medicines, and as 
these appear to have been dispensed gratuitously there 
was no lack of patients. 

Tycho's imperious and grasping character frequently 
brought him into diifficulties, which seem to have increased 
with his advancing years. He had ill-treated one of his 
tenants on Hven, and an adverse decision by the courts seems 
to have greatly exasperated the astronomer. Serious changes 
also took place in his relations to the court at Copen- 
hagen» When the young king was crowned in 1596, he 
reversed the policy of his predecessor with reference to 
Hven. The liberal allowances to Tycho were one after 
another withdrawn, and finally even his pension was 
stopped. Tycho accordingly abandoned Hven in a tumult 
of rage and mortification. A few years later we find 
him in Bohemia a prematurely aged man, and he died 
on the 24th October, 1601. 


Among the ranks of the great astronomers ifc would be 
difficult to find one whose life presents more interesting 
features and remarkable vicissitudes than does that of 
Galileo. We may consider him as the patient inves- 
tigator and brilliant discoverer. We may consider him 
in his private relations, especially to his daughter, Sister 
Maria Celeste, a woman of very remarkable character ; and 
we have also the pathetic drama at the close of Galileo's 
life, when the philosopher drew down upon himself the 
thunders of the Inquisition. 

The materials for the sketch of this astonishing man are 
sufficiently abundant. We make special use in this place 
of those charming letters which his daughter wrote to 
him from her convent home. More than a hundred of 
these have been preserved, and it may well be doubted 
whether any more beautiful and touching series of letters 
addressed to a parent by a dearly loved child have ever 
been written. An admirable account of this correspond- 
ence is contained in a little book entitled ** The Private 
Life of Galileo," published anonymously by Messrs. Mac- 
millan in 1870, and I have been much indebted to the 
author of that volume for many of the facts contained in 
this chapter. 


Galileo was born at Pisa, on ISth February, 1564. He 
was the eldest son of Vincenzo de' Bonajuti de' Galilei, 
a Florentine noble. Notwithstanding his illustrious birth 
and descent, it would seem that the home in which the 
great philosopher's childhood was spent was an im- 
poverished one. It was obvious at least that the young 
Galileo would have to be provided with some profession 
by which he might earn a livelihood. From his father 
he derived both by inheritance and by precept a keen 
taste for music, and it appears that he became an excel- 
lent performer on the lute. He was also endowed with 
considerable artistic power, which he cultivated diligently. 
Indeed, it would seem that for some time the future astro- 
nomer entertained the idea of devoting himself to painting 
as a profession. His father, however, decided that he 
should study medicine. Accordingly, we find that when 
Galileo was seventeen years of age, and had added a 
knowledge of Greek and Latin to his acquaintance with 
the fine arts, he was duly entered at the University 
of Pisa. 

Here the young philo5:opher obtained some inkling of 
mathematics, whereupon he became &o much interested in 
this branch of science, that he begged to be allowed to 
study geometry. In compliance with his request, his 
father permitted a tutor to be engaged for this purpose ; 
but he did so with reluctance, fearing that the attention 
of the young student might thus be withdrawn from that 
medical work which was regarded as his primary occupa- 
tion. The event speedily proved that these anxieties 
were not without some justification. The propositions of 
Euclid proved so engrossing to Galileo that it was thought 


wise to avoid further distraction by terminating the 
mathematical tutor's engagement. But it was too late 
for the desired end to be attained. Gralileo had now made 
such progress that he was able to continue his geometrical 
studies by himself. Presently he advanced to that famous 
47th proposition which won his lively admiration, and on 
he went until he had mastered the six books of Euclid, 
which was a considerable achievement for those days. 

The diligence and brilliance of the young student at 
Pisa did not, however, bring him much credit with the 
University authorities. In those days the doctrines of 
Aristotle were regarded as the embodiment of all human 
wisdom in natural science as well as in everything else. 
It was regarded as the duty of every student to learn 
Aristotle off by heart, and any disposition to doubt or 
even to question the doctrines of the venerated teacher 
was regarded as intolerable presumption. But young 
Galileo had the audacity to think for himself about the 
laws of nature. He would not take any assertion of fact 
on the authority of Aristotle when he had the means of 
questioning nature directly as to its truth or falsehood. 
His teachers thus came to regard him as a somewhat mis- 
guided youth, though they could not but respect the 
unflagging industry with which he amassed all the 
knowledge he could acquire. 

We are so accustomed to the use of pendulums in our 
clocks, that perhaps we do not often realise that the 
introduction of this method of regulating time-pieces was 
really a notable invention worthy the fame of the great 
astronomer to whom it was due. It appears that sitting 
one day in the Cathedral of Pisa, Galileo's attention 



Galileo's Pendulum. 

became concentrated on the swinging of a chandeliei 
which, hung from the ceiling. It struck him as a signifi- 
cant point, that whether the arc through w^hich the 
pendulum oscillated was a long one or a short one, the 
time occupied in each vibration was sensibly the same. 
This suggested to the thoughtful observer that a pen- 
dulum would afford the means by which a time-keeper 
might be controlled, and accordingly Galileo constructed 
for the first time a clock on this principle. The imme- 


diate object souglit in this apparatus was to provide a 
means of aiding physicians in counting the pulses of 
their patients. 

The talents of Galileo having at length extorted due 
recognition from the authorities, he was appointed, at 
the age of twenty-five. Professor of Mathematics at the 
University of Pisa. Then came the time when he felt 
himself strong enough to throw down the gauntlet to the 
adherents of the old philosophy. As a necessary part of 
his doctrine on the movement of bodies, Aristotle had 
asserted that the time occupied by a stone in falling 
depends upon its weight, so that the heavier the stone 
the less time would it require to fall from a certain 
height to the earth. It might have been thought that a 
statement so easily confuted by the simplest experiments 
could never have maintained its position in any accepted 
scheme of philosophy. But Aristotle had said it, and to 
any one who ventured to express a doubt the ready sneer 
was forthcoming, '' Do you think yourself a cleverer man 
than Aristotle ? " GaKleo determined to demonstrate in 
the most emphatic manner the absurdity of a doctrine 
which had for centuries received the sanction of the 
learned. The summit of the Leaning Tower of Pisa offered 
a highly dramatic site for the great experiment. The 
youthful professor let fall from the overhanging top a 
large heavy body and a small light body simultaneously. 
According to Aristotle the large body ought to have 
reached the ground much sooner than the small one, but 
such was found not to be the case. In the sight of a 
large concourse of people the simple fact was demon- 
strated that the two bodies fell side by side, and reached 


the ground at the same time. Thus the first great step 
was taken in the overthrow of that preposterous system 
of unquestioning adhesion to dogma, which had impeded 
the development of the knowledge of nature for nearly 
two thousand years. 

This revolutionary attitude towards the ancient beliefs 
was not calculated to render Galileo's relations with the 
University authorities harmonious. He had also the 
misfortune to make enemies in other quarters. Don 
Giovanni de Medici, who was then the Governor of the 
Port of Leghorn, had designed some contrivance by 
which he proposed to pump out a dock. But Galileo 
showed up the absurdity of this enterprise in such an 
aggressive manner that Don Giovanni took mortal oflPence, 
nor was he mollified when the truths of Galileo's criti- 
cisms were abundantly verified by the total failure of his 
ridiculous invention. In various ways Galileo was made 
to feel his position at Pisa so unpleasant that he was at 
length compelled to abandon his chair in the University. 
The active exertions of his friends, of whom Galileo was 
so fortunate as to have had throughout his life an abun- 
dant supply, then secured his election to the Professorship 
of Mathematics at Padua, whither he went in 1592. 

It was in this new position that Galileo entered on that 
marvellous career of investigation which was destined to 
revolutionize science. The zeal with which he discharged 
his professorial duties was indeed of the most unremitting 
character. He speedily drew such crowds to listen to his 
discourses on Natural Philosophy that his lecture-room 
was filled to overflowing. He also received many private 
pupils in his house for special instruction. Every moment 


Portrait of Gralileo. 

that could be spared from these labours was devoted to 
bis private study and to bis incessant experiments. 

Like many another philosopher who has greatly ex- 
tended our knowledge of nature, Galileo had a remark- 
able aptitude for the invention of instruments designed 
for philosophical research. To facilitate his practical 
work, we find that in 1599 he had engaged a skilled 


workman who was to live in his house, and thus be con- 
stantly at hand to try the devices for ever springing from 
Galileo's fertile brain. Among the earliest of his inven- 
tions appears to have been the thermometer, which he 
constructed in 1602. No doubt this apparatus in its 
primitive form differed in some respects from the con- 
trivance we call by the same name. Galileo at first em- 
ployed water as the agent, by the expansion of which the 
temperature was to be measured. He afterwards saw the 
advantage of using spirits for the same purpose. It was 
not until about half a century later that mercury came to 
be recognised as the liquid most generally suitable for the 

The time was now approaching when Galileo was to 

make that mighty step in the advancement of human 

1^ knowledge which followed on the application of the tele- 

\) scope to astronomy. As to how his idea of such an 

^ instrument originated, we had best let him tell us in his 

~T^ own words. The passage is given in a letter which he 

writes to his brother-in-law, Landucci. 

*' I write now because I have a piece of news for you, 
though whether you will be glad or sorry to hear it I 
cannot say ; for I have now no hope of returning to my 
own country, though the occurrence which has destroyed 
that hope has had results both useful and honourable. 
You mu;st know, then, that two months ago there was a 
report spread here that in Flanders some one had presented 
to Count Maurice of Nassau a glass manufactured in 
such a way as to make distant objects appear very near, so 
that a man at the distance of two miles could be clearly seen. 
This seemed to me so marvellous that I began to think 


about it. As it appeared to me to have a foundation in 
ttie Theory of Perspective, I set about contriving how to 
make it, and at length I found out, and have succeeded so 
well that the one I have made is far superior to the Dutch 
telescope. It was reported in Venice that I had made 
one, and a week since I was commanded to show it to his 
Serenity and to all the members of the senate, to their 
infinite amazement. Many gentlemen and senators, even 
the oldest, have ascended at various times the highest 
bell-towers in Venice to spy out ships at sea making sail 
for the mouth of the harbour, and have seen them clearly, 
though without my telescope they would have been in- 
visible for more than two hours. The effect of this 
instrument is to show an object at a distance of say fifty 
miles, as if it were but five miles." 

The remarkable properties of the telescope at once 
commanded universal attention among intellectual men. 
Galileo received applications from several quarters for his 
new instrument, of which it would seem that he manu- 
factured a large number to be distributed as gifts to 
various illustrious personages. 

But it was reserved for Galileo himself to make 
that application of the instrument to the celestial bodies 
by which its peculiar powers were to inaugurate the 
new era in astronomy. The first discovery that was 
made in this direction appears to have been connected 
with the number of the stars. Galileo saw to his amaze- 
ment that through his little tube he could count ten 
times as many stars in the sky as his unaided eye could 
detect.- Here was, indeed, a surprise. We are now so 
familiar with the elementary facts of astronomy that it 


is not always easy to realise liow tlie lieavens were 
interpreted by tlie observers in tbose ages prior to tbe 
invention of tbe telescope. We can bardly, indeed, 
suppose that Galileo, like the majority of those who ever 
thought of such matters, entertained the erroneous belief 
that the stars were on the surface of a sphere at equal 
distances from the observer. No one would be likely to 
have retained his belief in such a doctrine when he saw 
how the number of visible stars could be increased ten- 
fold by means of Galileo's telescope. It would have 
been almost impossible to refuse to draw the inference 
that the stars thus brought into view were still more 
remote objects which the telescope was able to reveal, 
just in the same way as it showed certain ships to the 
astonished Yenetians, when at the time these ships were 
beyond the reach of unaided vision. 

Galileo's celestial discoveries now succeeded each other 
rapidly. That beautiful Milky Way, which has for ages 
been the object of admiration to all lovers of nature, never 
disclosed its true nature to the eye of man till the astro- 
nomer of Padua turned on it his magic tube. The splen- 
did zone of silvery light was then displayed as star-dust 
scattered over the black background of the sky. It was 
observed that though the individual stars were too small 
to be seen severally without optical aid, yet such was 
their incredible number that the celestial radiance pro- 
duced that luminosity with which every star-gazer was so 

But the greatest discovery made by the telescope in 
these early days, perhaps, indeed, the greatest discovery 
that the telescope has ever accomplished, was the detec- 


tion of the system of four satellites revolving around the 
great planet Jupiter. This phenomenon was so wholly 
unexpected by Galileo that, at first, he could hardly 
believe his eyes. However, the reality of the existence 
of a system of four moons attending the great planet was 
soon established beyond all question. Numbers of great 
personages crowded to Galileo to see for themselves this 
beautiful miniature representing the sun with its system 
of revolving planets. 

Of course there were, as usual, a few incredulous people 
who refused to believe the assertion that four more mov- 
ing bodies had to be added to the planetary system. 
They scoffed at the notion ; they said the satellites may 
have been in the telescope, but that they were not in 
the sky. One sceptical philosopher is reported to have 
affirmed, that even if he saw the moons of Jupiter himself 
he would not believe in them, as their existence was con- 
trary to the principles of common-sense ! 

There can be no doubt that a special significance 
attached to the new discovery at this particular epoch in 
the history of science. It must be remembered that in 
those days the doctrine of Copernicus, declaring that the 
sun, and not the earth, was the centre of the system, that 
the earth revolved on its axis once a day, and that it 
described a mighty circle round the sun once a year, had 
only recently been promulgated. This new view of the 
scheme of nature had been encountered with the most 
furious opposition. It may possibly have been that 
Galileo himself had not felt quite confident in the sound- 
ness of the Copernican theory, prior to the discovery of 
the satellites of Jupiter. But when a picture was there 



exhibited in which a number of relatively small globes 
were shown to be revolving around a single large globe 
in the centre, it seemed impossible not to feel that the 
beautiful spectacle so displayed was an emblem of the 
relations of the planets to the sun. It was thus made 
manifest to Galileo that the Copernican theory of the 
planetary system must be the true one. The momentous 
import of this opinion upon the future welfare of the great 
philosopher will presently appear. 

It would seem that Galileo regarded his residence at 
Padua as a state of undesirable exile from his beloved 
Tuscany. He had always a yearning to go back to his 
own country, and at last the desired opportunity presented 
itself. For now that Galileo's fame had become so great, 
the Grand Duke of Tuscany desired to have the philo- 
sopher resident at Florence, in the belief that he would 
shed lustre on the Duke's dominions. Overtures were 
accordingly made to Galileo, and the consequence was 
that in 1616 we find him residing at Florence, bearing 
the title of Mathematician and Philosopher to the Grand 

Two daughters, Polissena and Virginia, and one son, 
Vincenzo, had been born to Galileo in Padua. It was 
the custom in those days that as soon as the daughter of 
an Italian gentleman had grown up, her future career was 
somewhat summarily decided. Either a husband was to 
be forthwith sought out, or she was to enter the convent 
with the object of taking the veil as a professed nun. It 
was arranged that the two daughters of Galileo, while still 
scarcely more than children, should both enter the Fran- 
ciscan convent of St. Matthew, at Arcetri. The elder 

GALILEO, - 79 

daughter, Polissena, took the name of Sister Maria 
Celeste, while Yirginia became Sister Arcangela. The 
latter seems to have been alwaj^s delicate and subject to 
prolonged melancholy, and she is of but little account in 
the narrative of the life of Galileo. But Sister Maria 
Celeste, though never leaving the convent, managed to 
preserve a close intimacy with her beloved father. This 
was maintained only partly by Galileo's visits, which 
were very irregular and were, indeed, often suspended 
for long intervals. But his letters to this daughter 
were evidently frequent and affectionate, especially in 
the latter part of his life. Most unfortunately, how- 
ever, all his letters have been lost. There are grounds 
for believing that they were deliberately destroyed when 
Galileo was seized by the Inquisition, lest they should 
have been used as evidence against him, or lest they should 
have compromised the convent where they were received. 
But Sister Maria Celeste's letters to her father have 
happily been preserved, and most touching these letters 
are. We can hardly read them without thinking how 
the sweet and gentle nun would have shrunk from the 
idea of their publication. 

Her loving little notes to her " dearest lord and father/' 
as she used affectionately to call Galileo, were almost in- 
variably accompanied by some gift, trifling it may be, but 
always the best the poor nun had to bestow. The tender 
grace of these endearing communications was all the more 
precious to him from the fact that the rest of Galileo's 
relatives were of quite a worthless description. He always 
acknowledged the ties of his kindred in the most generous 
way, but their follies and their vices, their selfishness and 


their importunities, were an incessant source of annoyance 
to him, almost to the last day of his life. 

On 19th December, 1625, Sister Maria Celeste writes : — ■ 

" I send two baked pears for these days of vigil. But 
as the greatest treat of all, I send you a rose, which ought 
to please you extremely, seeing what a rarity it is at this 
season; and with the rose you must accept its thorns, 
which represent the bitter passion of our Lord, whilst the 
green leaves represent the hope we may entertain that 
through the same sacred passion we, having passed 
through, the darkness of the short winter of our mortal 
life, may attain to the brightness and felicity of an 
eternal spring in heaven.'^ 

When the wife and children of Galileo's shiftless 
brother came to take up their abode in the philosopher's 
home, Sister Maria Celeste feels glad to think that her 
father has now some one who, however imperfectly, may 
fulfil the duty of looking after him. A graceful note on 
Christmas Eve accompanies her little gifts. She hopes 
that — 

" In these holy days the peace of God may rest on him 
and all the house. The largest collar and sleeves I mean 
for Albertino, the other two for the two younger boys, 
the little dog for baby, and the cakes for everybody, 
except the spice-cakes, which are for you. Accept the 
good- will which would readily do much more." 

The extraordinary forbearance with which Galileo con- 
tinually placed his time, his purse, and his influence at 
the service of those who had repeatedly proved them- 
selves utterly unworthy of his countenance, is thus com- 
mented on by the good nun : — 


" Now it seems to me, dearest lord and father, that 
your lordship is walking in the right path, since you take 
hold of every occasion that presents itself to shower con- 
tinual benefits on those who only repay you with ingrati- 
tude. This is an action which is all the more virtuous 
and perfect as it is the more difficult." 

When the plague was raging in the neighbourhood, 
the loving daughter's solicitude is thus shown : — 

"I send you two pots of electuary as a preventive 
against the plague. The one without the label consists 
of dried figs, walnuts, rue, and salt, mixed together with 
honey. A piece of the size of a walnut to be taken in the 
morning, fasting, with a little Greek wine." 

The plague increasing still more, Sister Maria Celeste 
obtained, with much difficulty, a small quantity of a re- 
nowned liqueur, made by Abbess Ursula, an exception- 
ally saintly nun. This she sends to her father with the 
words : — 

*'I pray your lordship to have faith in this remedy. 
For if you have so much faith in my poor miserable 
prayers, much more may you have in those of such a holy 
person ; indeed, through her merits you may feel sure of 
escaping all danger from the plague." 

Whether Galileo took the remedy we do not know, but 
at all events he escaped the plague. 

From Galileo's new home in Florence the telescope 
was again directed to the skies, and again did astounding 
discoveries reward the astronomer's labours. The great 
success which he had met with in studying Jupiter natu- 
rally led Galileo to look at Saturn. Here he saw a 
spectacle which was sufficiently amazing, though he failed 




The Villa Arcetri. 

Galileo's residence, where Milton visited him. 

to interpret it accurately. It was quite manifest that 
Saturn did not exhibit a simple circular disc like Jupiter, 
or like Mars. It seemed to Galileo as if the planet con- 
sisted of three bodies, a large globe in the centre, and a 
smaller one on each side. The enigmatical nature of the 
discovery led Galileo to announce it in an enigmatical 
manner. He published a string of letters which, when 
duly transposed, made up a sentence which affirmed that 
the planet Saturn was threefold. Of course we now 
know that this remarkable appearance of the planet 
was due to the two projecting portions of the ring. 
With the feeble power of Galileo's telescope, these seemed 
merely like small globes or appendages to the large 
central body. 


The last of Galileo's great astronomical discoveries 
related to the libration of the moon. I think that the 
detection of this phenomenon shows his aciiteness of obser- 
vation more remarkably than does any one of his other 
achievements with the telescope. It is well known that 
the moon constantly keej)s the same face turned towards 
the earth. When, however, careful measurements have 
been made with regard to the spots and marks on the 
lunar surface, it is found that there is a slight periodic 
variation which permits us to see now a little to the east 
or to the west, now a little to the north or to the south of 
the average lunar disc. 

But the circumstances which make the career of Galileo 
so especially interesting from the biographer's point of 
view, are hardly so much the triumphs that he won as 
the sufferings that he endured. The sufferings and the 
triumphs were, however, closely connected, and it is fit- 
ting that we should give due consideration to what was 
perhaps the greatest drama in the history of science. 

On the appearance of the immortal work of Copernicus, 
in which it was taught that the earth rotated on 
its axis, and that the earth, like the other planets, 
revolved round the sun, orthodoxy stood aghast. The 
Holy Eoman Church submitted this treatise, which 
bore the name " De Eevolutionibus Orbium Coelestium," 
to the Congregation of the Index. After due examination 
it was condemned as heretical in 1615. Galileo was sus- 
pected, on no doubt excellent grounds, of entertaining the 
objectionable views of Copernicus. He was accordingly 
privately summoned before Cardinal Bellarmine on 26th 
Pebruary, 1616, and duly admonished that he was on no 


account to teacli or to defend the obnoxious doctrines. 
Galileo was much distressed by this intimation. He felt 
it a serious matter to be deprived of the privilege of dis- 
coursing with his friends about the Copernican system, 
and of instructing his disciples in the principles of the 
great theory of whose truth he was perfectly convinced. 
It pained him, however, still more to think, devout Catholic 
as he was, that such suspicions of his fervent allegiance 
to his Church should ever have existed, as were implied 
by the words and monitions of Cardinal Bellarmine. 

In 1616, Galileo had an interview with Pope Paul Y., 
who received the great astronomer very graciously, and 
walked up and down with him in conversation for three- 
quarters of an hour. Galileo complained to his Holiness 
of the attempts made by his enemies to embarrass him 
with the authorities of the Church, but the Pope bade 
him be comforted. His Holiness had himself no doubts 
of Galileo's orthodoxy, and he assured him that the Con- 
gregation of the Index should give Galileo no further 
trouble so long as Paul V. was in the chair of St. Peter. 

On the death of Paul Y. in 1623, Maflteo Barberini was 
elected Pope, as Urban YIII. This new Pope, while a 
cardinal, had been an intimate friend of Galileo's, and had 
indeed written Latin verses in praise of the great astro- 
nomer and his discoveries. It was therefore not unnatural 
for Galileo to think that the time had arrived when, with 
the use of due circumspection, he might continue his 
studies and his writings, without fear of incurring the 
displeasure of the Church. Indeed, in 1624, one of 
Galileo's friends writing from Rome, urges Galileo to 
visit the city again, and added that — 


"Under the auspices of this most excellent, learned, 
and benignant Pontiff, science must flourish. Your arrival 
will be welcome to his Holiness. He asked me if you 
were coming, and when, and in short, he seems to love 
and esteem you more than ever.'* 

The visit was duly paid, and when Galileo returned to 
Florence, the Pope wrote a letter from which the follow- 
ing is an extract, commending the philosopher to the 
good offices of the young Ferdinand, who had shortly 
before succeeded his father in the Grand Duchy of 

" We find in Galileo not only literary distinction, but 
also the love of piety, and he is also strong in those 
qualities by which the pontifical good-will is easily 
obtained. And now, when he has been brought to this 
city to congratulate us on our elevation, we have very 
lovingly embraced him ; nor can we suffer him to return 
to the country whither your liberality calls him, without 
an ample provision of pontifical love. And that you may 
know how dear he is to us, we have willed to give him 
this honourable testimonial of virtue and piety. And we 
further signify that every benefit which you shall confer 
upon him, imitating or even surpassing your father's 
liberality, will conduce to our gratification.'' 

The favourable reception which had been accorded to 
him by Pope Urban YIII. seems to have led Galileo to 
expect that there might be some corresponding change in 
the attitude of the Papal authorities on the great question 
of the stability of the earth. He accordingly proceeded 
with the preparation of the chief work of his life, " The 
Dialogue of the two Systems." It was submitted for 


inspection by tlie constituted authorities. The Pope him- 
self thought that, if a few conditions which he laid 
down were duly complied with, there could be no objec- 
tion to the publication of the work. In the first place, 
the title of the book was to be so carefully worded as to 
show plainly that the Copernican doctrine was merely to 
be regarded as an hypothesis, and not as a scientific fact. 
Galileo was also instructed to conclude the book with 
special arguments which had been supplied by the Pope 
himself, and which appeared to his Holiness to be quite 
conclusive against the new doctrine of Copernicus. 

Pormal leave for the publication of the Dialogue was 
then given to Galileo by the Inquisitor General, and it 
was accordingly sent to the press. It might be thought 
that the anxieties of the astronomer about his book would 
then have terminated. As a matter of fact, they had not 
yet seriously begun. Hiccardi, the Master of the Sacred 
Palace, having suddenly had some further misgivings, 
sent to Galileo for the manuscript while the work was at 
the printer's, in order that the doctrine it implied might 
be once again examined. Apparently, Kiccardi had come 
to the conclusion that he had not given the matter suffi- 
cient attention, when the authority to go to press had 
been first and, perhaj)s, hastily given. Considerable 
delay in the issue of the book was the result of these 
further deliberations. At last, however, in June, 1632, 
Galileo's great work, " The Dialogue of the two Systems," 
was produced for the instruction of the world, though the 
occasion was fraught with ruin to the immortal author. 

The book, on its publication, was received and read 
with the greatest avidity. But presently the Master of 



the Sacred Palace found reason to regret that he had 
given his consent to its appearance. He accordingly issued 
a peremptory order to sequestrate every copy in Italy. 
This sudden change in the Papal attitude towards Galileo 
formed the subject of a strong remonstrance addressed 
to the Roman authorities by the Grand Duke of Tuscany. 
The Pope himself seemed to have become impressed all at 
once with the belief that the work contained matter of an 

Facsimile Sketcli of Lunar Surface by Galileo. 

heretical description. The general interpretation put 
upon the book seems to have shown the authorities that 
they had mistaken its true tendency, notwithstanding the 
fact that it had been examined again and again by theolo- 
gians deputed for the duty. To the communication from 
the Grand Duke the Pope returned answer, that he had 
decided to submit the book to a congregation of *' learned, 
grave, and saintly men,'^ who would weigh every word in 


it. The views of his Holiness personally on the subject 
were expressed in his belief that the Dialogue contained 
the most perverse matter that could come into a reader's 

The Master of the Sacred Palace was greatly blamed by 
the authorities for having given his sanction to its issue. He 
pleaded that the book had not been printed in the precise 
terms of the original manuscript which had been submitted 
to him. It was also alleged that Galileo had not adhered 
to his promise of inserting properly the arguments which 
the Pope himself had given in support of the old and 
orthodox view. One of these had, no doubt, been intro- 
duced, but, so far from mending Galileo's case, it had 
made matters really look worse for the poor philosopher. 
The Pope's argument had been put into the mouth of one 
of the characters in the Dialogue named "Simplicio." 
Galileo's enemies maintained that by adopting such a 
method for the expression of his Holiness's opinion, Gali- 
leo had intended to hold the Pope himself up to ridicule. 
Galileo's friends maintained that nothing could have been 
farther from his intention. It seems, however, highly 
probable that the suspicions thus aroused had something 
to say to the sudden change of front on the part of the 
Papal authorities. 

On 1st October, 1632, Galileo received an order to 
appear before the Inquisition at Rome on the grave charge 
of heresy. Galileo, of course, expressed his submission, 
but pleaded for a respite from compliance with the sum- 
mons, on the ground of his advanced age and his failing 
health. The Pope was, however, inexorable ; he said 
that he had warned Galileo of his danger while he was 


still his friend. The command could Jiot be disobeyed. 
Galileo might perform the journey as slowly as he pleased, 
but it was imperatively necessary for him to set forth, and 
at once. 

On 20th January, 1633, Galileo started on his weary 
journey to Rome, in compliance with this peremptory 
summons. On 13th February he was received as the 
guest of Niccolini, the Tuscan -ambassador, who had acted 
as his wise and ever-kind friend throughout the whole 
affair. It seemed plain that the Holy Office were inclined 
to treat Galileo with as much clemency and consideration 
as was consistent with the determination that the case 
against him should be proceeded with to the end. The 
Pope intimated that in consequence of his respect for the 
Grand Duke of Tuscany he should permit Galileo to enjoy 
the privilege, quite unprecedented for a prisoner charged 
with heresy, of remaining as an inmate in the ambassa- 
dor's house. He ought, strictly, to have been placed in 
the dungeons of the Inquisition. When the examination 
of the accused had actually commenced, Galileo was con- 
fined, not, indeed, in the dungeons, but in comfortable 
rooms at the Holy Office. 

By the judicious and conciliatory language of sub- 
mission which Niccolini had urged Galileo to use before 
the Inquisitors, they were so far satisfied that they inter- 
ceded with the Pope for his release. During the remain- 
der of the trial Galileo was accordingly permitted to go 
back to the ambassador's, where he was most heartil}^ wel- 
comed. Sister Maria Celeste, evidently thinking this 
meant that the whole case was at an end, thus expresses 
herself : — 


" The joy that your last dear letter brought me, and the 
having to read it over and over to the nuns, who made 
quite a jubilee on hearing its contents, put me into such an 
excited state that at last I got a severe attack of headache/* 

In his defence Galileo urged that he had already been 
acquitted in 1616 by Cardinal Bellarmine, when a charge 
of heresy was brought against him, and he contended 
that anything he might now have done, was no more 
than he had done on the preceding occasion, when the 
orthodoxy of his doctrines received solemn confirmation. 
The Inquisition seemed certainly inclined to clemency, but 
the Pope was not satisfied. Galileo was accordingly sum- 
moned again on the 21st June. He was to be threatened 
with torture if he did not forthwith give satisfactory 
explanations as to the reasons which led him to write the 
Dialogue. In this proceeding the Pope assured the Tuscan 
ambassador that he was treating Galileo with the utmost 
consideration possible in consequence of his esteem and 
regard for the Grand Duke, whose servant Galileo was. 
It was, however, necessary that some exemplary punish- 
ment be meted out to the astronomer, inasmuch as by the 
publication of the Dialogue he had distinctly disobeyed 
the injunction of silence laid upon him by the decree of 
1616. Nor was it admissible for Galileo to plead that his 
book had been sanctioned by the Master of the Sacred 
College, to whose inspection it had been again and again 
submitted. It was held, that if the Master of the Sacred 
College had been unaware of the solemn warning the 
philosopher had already received sixteen years previously, 
it was the duty of Galileo to have drawn his attention to 
that fact. 


On the 22nd June, 1633, Galileo was led to the great 
hall of the Inquisition, and compelled to kneel before 
the cardinals there assembled and hear his sentence. In 
a long document, most elaborately drawn up, it is definitely 
charged against Galileo that, in publishing the Dialogue, 
he committed the essential^ grave error of treating the 
doctrine of the earth's motion as open to discussion. Gali- 
leo knew, so the document affirmed, that the Church had 
emphatically pronounced this notion to be contrary to 
Holy Writ, and that for him to consider a doctrine so 
stigmatized as having any shadow of probability in its 
favour was an act of disrespect to the authority of the 
Church which could not be overlooked. It was also 
charged against Galileo that in his Dialogue he has put 
the strongest arguments into the mouth, not of those who 
supported the orthodox doctrine, but of those who held 
the theory as to the earth's motion which the Church had 
so deliberately condemned. 

After due consideration of the defence made by the 
prisoner, it was thereupon decreed that he had rendered 
himself vehemently suspected of heresy by the Holy 
Office, and in consequence had incurred all the censures 
and penalties of the sacred canons, and other decrees 
promulgated against such persons. The graver portion of 
these punishments would be remitted, if Galileo would 
solemnly repudiate the heresies referred to by an abju- 
ration to be pronounced by him in the terms laid down. 

At the same time it was necessary to mark, in some 
emphatic manner, the serious offence which had been 
committed, so that it might serve both as a punishment to 
Galileo and as a warning to others. It was accordingly 


decreed that lie should be condemned to imprisonment in 
the Holy Office during the pleasure of the Papal autho- 
rities, and that he should recite once a week for three years 
the seven Penitential Psalms. 

Then followed that ever-memorable scene in the great 
hall of the Inquisition, in which the aged and infirm 
Galileo, the inventor of the telescope and the famous 
astronomer, knelt down to abjure before the most eminent 
and reverend Lords Cardinal, Inquisitors General 
throughout the Christian Eepublic against heretical de- 
pravity. With his hands on the Gospels, Galileo was 
made to curse and detest the false opinion that the sun 
was the centre of the universe and immovable, and that 
the earth was not the centre of the same, and that it 
moved. He swore that for the future he will never say 
nor write such things as may bring him under suspicion, 
and that if he does so he submits to all the pains and 
penalties of the sacred canons. This abjuration was sub- 
sequently read in Florence before Galileo's disciples, who 
had been specially summoned to attend. 

It has been noted that neither on the first occasion, in 
1616, nor on the second in 1633, did the reigning Pope 
sign the decrees concerning Galileo. The contention has 
accordingly been made that Paul Y. and Urban YIII. are 
both alike vindicated from any technical responsibility 
for the attitude of the Eomish Church towards the Coper- 
nican doctrines. The significance of this circumstance 
has been commented on in connection with the doctrine 
of the infallibility of the Pope. 

"We can judge of the anxiety felt by Sister Maria 
Celeste about her beloved father during these terrible 


trials. The wife of the ambassador Niccolini, Galileo's 
steadfast friend, most kindly wrote to give the nun what- 
ever quieting assurances the case would permit. There 
is a renewed flow of these touching epistles from the 
dauofhter to her father. Thus she sends word — 

** The news of your fresh trouble has pierced my soul 
with grief all the more that it came quite unexpectedly." 

And again, on hearing that he had been permitted to 
leave E-ome, she writes — - 

"I wish I could describe the rejoicing of all the 
mothers and sisters on hearing of your happy arrival at 
Siena. It was indeed most extraordinary. On hearing 
the news the Mother Abbess and many of the nuns ran to 
me, embracing me and weeping for joy and tenderness." 

The sentence of imprisonment was at first interpreted 
leniently by the Pope. Galileo was allowed to reside in 
qualified durance in the archbishop's house at Siena. 
Evidently the greatest pain that he endured arose from 
the forced separation from that daughter, whom he had 
at last learned to love with an affection almost comparable 
with that she bore to him. She had often told him that 
she never had any pleasure equal to that with which she 
rendered any service to her father. To her joy, she dis- 
covers that she can relieve him from the task of reciting 
the seven Penitential Psalms which had been imposed as 
a penance : — 

" I began to do this a while ago," sh^ writes, " and it 
gives me much pleasure. First, because I am persuaded 
that prayer in obedience to Holy Church must be effica- 
cious ; secondly, in order to save you the trouble of 
remembering it. If I had been able to do more, most 



willingly would I have entered a straiter prison tlian tlie 
one I live in now, if by so doing I could have set you at 

Sister Maria Celeste was gradually failing in health, 
but the great privilege was accorded to her of being able 
once again to embrace her beloved lord and master. 
Galileo had, in fact, been permitted to return to his old 
home ; but on the very day when he heard of his daughter's 

Crest of Galileo's Family. 

death came the final decree directing him to remain in his 
own house in perpetual solitude. 

Amid the advancing infirmities of age, the isolation 
from friends, and the loss of his daughter, Galileo once 
again sought consolation in hard work. He commenced 
his famous dialogue on Motion. Gradually, however, 
his sight began to fail, and blindness was at last added 
to his other troubles. On January 2ndj 1638, he writes 
to Diodati : — • 


" Alas, your dear friend and servant, Galileo, has been 
for the last month perfectly blind, so that this heaven, this 
earth, this universe, which I by my marvellous discoveries 
and clear demonstrations have enlarged a hundred thousand 
times beyond the belief of the wise men of bygone ages, 
henceforward is for me shrunk into such a small space as 
is filled by my own bodily sensations.'' 

But the end was approaching — the great philosopher, 
was attacked by low fever, from which he died on the 8th 
Januarv, 1G43. 


While tlie illustrious astronomer, Tycho Brahe, lay on his 
death-bed, lie had an interview which must ever rank as 
one of the important incidents in the history of science. 
The life of Tycho had been passed, as we have seen, in 
the accumulation of vast stores of careful observations of 
the positions of the heavenly bodies. It was not given to 
him to deduce from his splendid work the results to 
which they were destined to lead. It was reserved for 
another astronomer to distil, so to speak, from the volumes 
in which Tycho' s figures were recorded, the great truths 
of the universe which those figures contained. Tycho felt 
that his work required an interpreter, and he recognised 
in the genius of a young man with whom he was 
acquainted the agent by whom the world was to be taught 
some of the great truths of nature. To the bedside of the 
great Danish astronomer the youthful philosopher was 
summoned, and with his last breath Tycho besought of 
him to spare no labour in the performance of those calcu- 
lations, by which alone the secrets of the movements of 
the heavens could be revealed. The solemn trust thus 
imposed was duly accepted, and the man who accepted it 
bore the immortal name of Kepler, 


Kepler was born on the 27tli December, 1571, at Weil, 
in tbe Ducby of Wiirtemberg. It would seem tbat tbe 
circumstances of bis cbildbood must have been singularly- 
unhappy. His father, sprung from a well-connected family, 
was but a shiftless and idle adventurer ; nor was the 
great astronomer much more fortunate in his other parent. 
His mother was an ignorant and ill-tempered woman ; 
indeed, the ill-assorted union came to an abrupt end 
through the desertion of the wife h^ her husband when 
their eldest son John, the hero of our present sketch, was 
eighteen years old. The childhood of this lad, destined 
for such fame, was still further embittered by the circum- 
stance that when he was four years old he had a severe 
attack of small-pox. ISTot only was his eyesight perma- 
nently injured, but even his constitution appears to have 
been much weakened by this terrible malady. 

It seems, however, that the bodily infirmities of young 
John Kepler were the immediate cause of his attention 
being directed to the pursuit of knowledge. Had the boy 
been fitted like other boys for ordinary manual work, 
there can be hardly any doubt that to manual work his 
life must have been devoted. But, though his body was 
feeble, he soon gave indications of the possession of con- 
siderable mental power. It was accordingly thought that 
a suitable sphere for his talents might be found in the 
Church, which, in those days, was almost the only pro- 
fession that afi'orded an opening for an intellectual 
career. We thus find that by the time John Kepler was 
seventeen years old he had attained a sufficient standard 
of knowledge to entitle him to admission on the foundation 
of the University at Tiibingen. 


In the course of his studies at this institution he seems 
to have divided his attention equally between astronomy 
and divinity. It not unfrequently happens that when a 
man has attained considerable proficiency in two branches 
of knowledge he is not able to see very clearly in which 
of the two pursuits his true vocation lies. His friends 
and onlookers are often able to judge more wisely than he 
himself can do as to which of the two lines it would be 
better for him to pursue. This incapacity for perceiving 
the path in which greatness awaited him, existed in the 
case of Kepler. Personally, he inclined to enter the 
ministry, in which a promising career seemed open to 
him. He yielded, however, to friends, who evidently 
knew him better than he knew himself, and accepted, 
in 1594, the important professorship of astronomy 
which had been offered to him in the University of 

It is difficult for us in these modern days to realise the 
somewhat extraordinary duties which were expected from 
an astronomical professor in the sixteenth century. He 
was, of course, required to employ his knowledge of the 
heavens in the prediction of eclipses, and of the move- 
ments of the heavenly bodies generally. This seems 
reasonable enough ; but what we are not prepared to 
accept is the obligation which lay on the astronomers to 
predict the fates of nations and the destinies of indivi- 

It must be remembered that it was the almost uni- 
versal belief in those days, that all the celestial spheres 
revolved in some mysterious fashion around the earth, 
which appeared by far the most important body in the 


universe. It was imagined that tlie sun, the moon, and 
the stars indicated, in the vicissitudes of their movements, 
the careers of nations and of individuals. Such being the 
generally accepted notion, it seemed to follow that a 
professor who was charged with the duty of expounding 
the movements of the heavenly bodies must necessarily be 
looked to for the purpose of deciphering the celestial 
decrees regarding the fate of man which the heavenly 
luminaries were designed to announce. 

Kepler threw himself with characteristic ardour into 
even this fantastic phase of the labours of the astronomical 
professor ; he diligently studied the rules of astrology, 
which the fancies of antiquity had compiled. Believing 
sincerely as he did in the connection between the aspect 
of the stars and the state of human affairs, he even 
thought that he perceived, in the events of his own life, a 
corroboration of the doctrine which affirmed the influence 
of the planets upon the fate of individuals. 

But quite independently of astrology there seem to 
have been many other delusions current among the philo- 
sophers of Kepler's time. It is now almost incomprehen- 
sible how the ablest men of a few centuries ago should 
have entertained such preposterous notions, as they did, 
with respect to the system of the universe. As an in- 
stance of what is here referred to, we may cite the extra- 
ordinary notion which, under the designation of a discovery, 
first brought Kepler into fame. Geometers had long 
known that there were five, but no more than five, regular 
solid figures. There is, for instance, the cube with six 
sides, which is, of course, the most familiar of these 
solids. Besides the cube there are other figures of foui-, 



Kepler's system of regular solids. 

eight, twelve, and twenty sides respectively. It also 
happened that there were five planets, but no more than 
five, known to the ancients, namely. Mercury, Yenus, 
Mars, Jupiter, and Saturn. To Kepler's lively imagina- 
tions this coincidence suggested the idea that the five 
regular solids corresponded to the five planets, and a 
number of fancied numerical relations were adduced on 
the subject. The absurdity of this doctrine is obvious 
enough, especially when we observe that, as is now 
well known, there are two large planets, and a host of 
small planets, over and above the magical number of the 
regular solids. In Kepler's time, however, this doctrine 
was so far from being regarded as absurd, that its 
announcement was hailed as a great intellectual triumph. 
Kepler was at once regarded with favour. It seems, 
indeed, to have been the circumstance which brought him 
into correspondence with Tycho Brahe. By its means 
also he became known to Galileo. 

KEPLER. loi 

The career of a scientific professor in those early days 
appears generally to have been marked by rather more 
striking vicissitudes than usually befall a professor in a 
modern university. Kepler was a Protestant, and as such 
he had been appointed to his professorship at Gratz. A 
change, however, having taken place in the religious 
belief entertained by the ruling powers of the University, 
the Protestant professors were expelled. It seems that 
special influence having been exerted in Kepler's case on 
account of his exceptional eminence, he was recalled to 
Gratz, and reinstated in the tenure of his chair. But 
his pupils had vanished, so that the great astronomer was 
glad to accept a post offered him by Tycho Brahe in the 
observatory which the latter had recently established near 

On Tycho's death, which occurred soon after, an 
opening presented itself which gave Kepler the oppor- 
tunity his genius demanded. He was appointed to 
succeed Tycho in the position of imperial mathematician. 
But a far more important point, both for Kepler and for 
science, was that to him was confided the use of Tycho's 
observations. It was, indeed, by the discussion of Tycho's 
results that Kepler was enabled to make the discoveries 
which form such an important part of astronomical 

Kepler must also be remembered as one of the first 
great astronomers who ever had the privilege of viewing 
celestial bodies through a telescope. It was in 1610 that 
he first held in his hands one of those little instruments 
which had been so recently applied to the heavens by 
Galileo. It should, however, be borne in mind that the 


epocli-making achievements of Kepler did not arise from 
any telescopic observations that lie made, or, indeed, that 
any one else made. They ^were all elaborately deduced 
from Tycho's measurements of the positions of the planets, 
obtained with his great instruments, which were unpro- 
vided with telescopic assistance. 

To realise the tremendous advance which science received 
from Kepler's great work, it is to be understood that all 
the astronomers who laboured before him at the difficult 
subject of the celestial motions, took it for granted that 
the planets must revolve in circles. If it did not ap- 
pear that a planet moved in a fixed circle, then the ready 
answer was provided by Ptolemy's theory that the circle 
in which the planet did move was itself in motion, so that 
its centre described another circle. 

When Kepler had before him that wonderful series of 
observations of the planet. Mars, which had been accumu- 
lated by the extraordinary skill of Tycho, he proved, after 
much labour, that the movements of the planet refused to 
be represented in a circular form. IN^or would it do to 
suppose that Mars revolved in one circle, the centre of 
which revolved in another circle. On no such supj)Osition 
could the movements of the planets be made to tally with 
those which Tycho had actually observed. This led to the 
astonishing discovery of the true form of a planet's orbit. 
Por the first time in the history of astronomy the prin- 
ciple was laid down that the movement of a planet could 
not be represented by a circle, nor even by combinations 
of circles, but that it could be represented by an elliptic 
path. In this path the sun is situated at one of those 
two points in the ellipse which are known as its foci. 



Very simple apparatus is needed for the drawing of one 
of those ellipses which Kepler has shown to possess such 
astonishing astronomical significance. Two pins are stuck 


through a sheet of paper on a board, the point of a pencil 
is inserted in a loop of string which passes over the pins, 
and as the pencil is moved round in such a way as to 


keep the string stretched, that beautiful curve known as 
the ellipse is delineated, while the positions of the pins 
indicate the two foci of the curve. If the length of the 
loop of string is unchanged then the nearer the pins are 
together, the greater will be the resemblance between the 
ellipse and the circle, whereas the more the pins are 
separated the more elongated does the ellipse become. 
The orbit of a great planet is, in general, one of those 
ellipses which approaches a nearly circular form. It for- 
tunately happens, however, that the orbit of Mars makes 
a wider departure from the circular form than any of the 
other important planets. It is, doubtless, to this circum- 
stance that we must attribute the astonishing success of 
Kepler in detecting the true shape of a planetary orbit. 
Tycho's observations would not have been sufficiently 
accurate to have exhibited the elliptic nature of a plane- 
tary orbit which, like that of Yenus, differed very little 
from a circle. 

The more we ponder on this memorable achievement 
the more striking will it appear. It must be remembered 
that in these days we know of the physical necessity 
which requires that a planet shall revolve in an ellipse 
and not in any other curve. But Kepler had no such 
knowledge. Even to the last hour of his life he remained 
-m ignorance of the existence of any natural cause which 
ordained that planets should follow those particular curves 
which geometers know so well. Kepler's assignment of 
the ellipse as the true form of the planetary orbit is to be 
regarded as a brilliant guess, the truth of which Tycho's 
observations enabled him to verify. Kepler also suc- 
ceeded in pointing out the law according to which the 

KEPLER. 105 

velocity of a planet at different points of its path could 
be accurately specified. Here, again, we have to admire 
the sagacity with which this marvellously acute astro- 
nomer guessed the deep truth of nature. In this case 
also he was quite unprovided with any reason for expect- 
ing from physical principles that such a law as he dis- 
covered must be obeyed. It is quite true that Kepler 
had some slight knowledge of the existence of what we 
now know as gravitation. He had even enunciated the 
remarkable doctrine that the ebb and flow of the tide 
must be attributed to the attraction of the moon on the 
waters of the earth. He does not, however, appear to 
have had any anticipation of those wonderful discoveries 
which IN^ewton was destined to make a little later, in which 
he demonstrated that the laws detected by Kepler's 
marvellous acumen were necessary consequences of the 
principle of universal gravitation. 

To appreciate the relations of Kepler and Tycho it is 
necessary to note the very different way in which these 
illustrious astronomers viewed the system of the heavens. 
It should be observed that Copernicus had already ex- 
pounded the true system, which located the sun at the 
centre of the planetary system. But in the days of Tycho 
Brahe this doctrine had not as yet commanded universal 
assent. In fact, the great observer himself did not accept 
the new views of Copernicus. It appeared to Tycho that 
the earth not only appeared to be the centre of things 
celestial, but that it actually was the centre. It is, 
indeed, not a little remarkable that a student of the 
heavens so accurate as Tycho should have deliberately 
rejected the Copernican doctrine in favour of the system 



wMcli now seems so j)reposterous. Tliroiigliout his great 
career, Tycho steadily observed tlie places of the sun, the 
moon, and the planets, and as steadily maintained that all 
those bodies revolved around the earth fixed in the centre. 
Kepler, however, had the advantage of belonging to the 
new school. He utilised the observations of Tycho in 

Symbolical representation of the planetary system . 

developing the great Copernican theory whose teaching 
Tycho stoutly resisted. 

Perhaps a chapter in modern science may illustrate the 
intellectual relation of these great men. The revolution 
produced by Copernicus in the doctrine of the heavens 
has often been likened to the revolution which the Dar- 

KEPLER, - 107 

winian theory produced in the views held by biologists as 
to life on this earth. The Darwinian theory did not at 
first command universal assent even among those natural- 
ists whose lives had been devoted with the greatest success 
to the study of organisms. Take, for instance, that great 
naturalist, Professor Owen, by whose labours vast exten- 
sion has been given to our knowledge of the fossil animals 
which dwelt on the earth in past ages. Now, though 
Owen's researches were intimately connected with the 
great labours of Darwin, and afforded the latter material 
for his epoch-making generalization, yet Owen deliber- 
ately refused to accept the new doctrines. Like Tycho, 
he kept on rigidly accumulating his facts under the in- 
fluence of a set of ideas as to the origin of living forms 
which are now universally admitted to be erroneous. If, 
therefore, we liken Darwin to Copernicus, and Owen to 
Tycho, we may liken the biologists of the present day to 
Kepler, who interpreted the results of accurate observa- 
tion upon sound theoretical principles. 

In reading the works of Kepler in the light of our 
modern knowledge we are often struck by the extent to 
which his perception of the sublimest truths in nature 
was associated with the most extravagant errors and 
absurdities. But, of course, it must be remembered 
that he wrote in an age in which even the rudiments of 
science, as we now understand it, were almost entirely 

It may well be doubted whether any joy experienced by 
mortals is more genuine than that which rewards the success- 
ful searcher after natural truths. Every science-worker, 
be his efforts ever so humble, will be able to sympathise 


with, the enthusiastic delight of Kepler wlien at last, after 
years of toil, the glorious light broke forth, and tliat which, 
he considered to be the greatest of his astonishing laws 
first dawned upon him. Kepler rightly judged that the 
number of days which a planet required to perform its 
voyage round the sun must be connected in some manner 
with the distance from the planet to the sun ; that is to 
say, with the radius of the planet's orbit, inasmuch as we 
may for our present object regard the planet's orbit as 

Here, again, in his search for the unknown law, Kepler 
had no accurate dynamical principles to guide his steps. 
Of course, we now know not only what the connection be- 
tween the planet's distance and the planet's periodic time 
actually is, but we also know that it is a necessary con- 
sequence. of the law of universal gravitation. Kepler, it 
is true, was not without certain surmises on the subject, 
but they were of the most fanciful description. His 
notions of the planets, accurate as they were in certain 
important respects, were mixed up with vague ideas as to 
the properties of metals and the geometrical relatioDs of 
the regular solids. Above all, his reasoning was pene- 
trated by the supposed astrological influences of the stars 
and their significant relation to human fate. Under the 
influence of such a farrago of notions, Kepler resolved to 
make all sorts of trials in his search for the connection 
between the distance of a planet from the sun and the 
time in which the revolution of that planet was accom- 

It was quite easily demonstrated that the greater the 
distance of the planet from the sun the longer was the 

KEPLER. 109 

time required for its journey. It might have been 
thought that the time would be directly proportional to 
the distance. It was, however, easy to show that this 
supposition did not agree with the fact. Finding that 
this simple relation would not do, Kepler undertook a vast 
series of calculations to find out the true method of ex- 
pressing the connection. At last, after many vain 
attempts, he found, to his indescribable joy, that the 
square of the time in which a planet revolves around the 
sun was proportional to the cube of the average distance 
of the planet from that body. 

The extraordinary way in which Kepler's views on 
celestial matters were associated with the wildest specula- 
tions, is well illustrated in the work in which he pro- 
pounded his splendid discovery just referred to. The 
announcement of the law connecting the distances of the 
planets from the sun with their periodic times, was then 
mixed up with a preposterous conception about the pro- 
perties of the different planets. They were supposed to 
be associated with some profound music of the spheres 
inaudible to human ears, and performed only for the 
benefit of that being whose soul formed the animating 
spirit of the sun. 

Kepler was also the first astronomer who ever ventured 
to predict the occurrence of that remarkable phenomenon, 
the transit of a planet in front of the sun's disc. He pub- 
lished, in 1629, a notice to the curious in things celestial, 
in which he announced that both of the planets. Mercury 
and Yenus, were to make a transit across the sun on 
specified days in the winter of 1631. The transit of 
Mercury was duly observed by Gassendi, and the 


transit of Yenus also took place, though, as we now know, 
the circumstances were such that it was not possible 
for the phenomenon to be witnessed by any European 

In addition to Kepler's discoveries already mentioned, 
with which his name will be for ever associated, his claim 
on the gratitude of astronomers chiefly depends on the 
publication of his famous Rudolphine tables. In this re- 
markable work means are provided for finding the places 
of the planets with far greater accuracy than had pre- 
viously been attainable. 

Kepler, it must be always remembered, was not an 
astronomical observer. It was his function to deal with 
the observations made by Tycho, and, from close study 
and comparison of the results, to work out the move- 
ments of the heavenly bodies. It was, in fact, Tycho 
who provided as it were the raw material, while it was 
the genius of Kepler which wrought that material into 
a beautiful and serviceable form. For more than a cen- 
tury the Rudolphine tables were regarded a^s a standard 
astronomical work. In these days we are accustomed 
to find the movements of the heavenly bodies set forth 
with all desirable exactitude in the Nautical Almanack , 
and the similar publication issued by foreign Grovernments. 
Let it be remembered that it was Kepler who first imparted 
the proper impulse in this direction. 

Y»^hen Kepler was twenty-six he married an heiress 
from Styria, who, though only twenty-three years old, 
had already had some experience in matrimony. Her 
first husband had died ; and it was after her second hus- 
band had divorced her that she received the addresses of 



The Commemoration of the Riadolphine Tables. 


Kepler. It will not be surprising to hear that his 
domestic affairs do not appear to have been particularly 
happy, and his wife died in 1611. Two years later, un- 
deterred by the want of success in his first venture, he 
sought a second partner, and he evidently determined 
not to make a mistake this time. Indeed, the methodical 
manner in which he made his choice of the lady to whom 
he should propose has been duly set forth by him and pre- 
served for our edification. With some self-assurance he 
asserts that there were no fewer than eleven spinsters 
desirous of sharing his joys and sorrows. He has care- 
fully estimated and recorded the merits and demerits of 
each of these would-be brides. The result of his delibera- 
tions was that he awarded himself to an orphan girl, 
destitute even of a portion. Success attended his choice, 
and his. second marriage seems to have proved a much 
more suitable union than his first. He had five children by 
the first wife and seven by the second. 

The years of Kepler's middle life were sorely distracted 
by a trouble which, though not uncommon in those days, 
is one which we find it difficult to realise at the present 
time. His mother, Catherine Kepler, had attained unde- 
sirable notoriety by the suspicion that she was guilty of 
witchcraft. Years were spent in legal investigations, and 
it was only after unceasing exertions on the part of the 
astronomer for upwards of a twelvemonth that he was 
finally able to procure her acquittal and release from 

It is interesting for us to note that at one time there 
was a proposal that Kepler should forsake his native 
country and adopt England as a home. It arose in this 

KEPLER, 113 

wise. Tlie great man was distressed througliout the 
greater part of his life by pecuniary anxieties. Finding 
him in a strait of this description, the English ambassador 
in Venice, Sir Henry "Wotton, in the year 1620, besought 
Kepler to come over to England, where he assured him 
that he would obtain a favourable reception, and where, 
he was able to add, Kepler's great scientific work was 
already highly esteemed. But his efforts were unavail- 
ing ; Kepler would not leave his own country. He was 
then forty-nine years of age, and doubtless a home in a 
foreign land, where people spoke a strange tongue, had 
not sufficient attraction for him, even when accompanied 
with the substantial inducements which the ambassador 
was able to offer. Had Kepler accepted this invitation, 
he would, in transferring his home to England, have 
anticipated the similar change which took place in the 
career of another great astronomer two centuries later. 
It will be remembered that Herschel, in his younger 
days, did transfer himself to England, and thus gave to 
England the imperishable fame of association with his 

The publication of the Kudolphine tables of the celestial 
movements entailed much expense. A considerable part 
of this was defrayed by the Government at Venice, but 
the balance occasioned no little trouble and anxiety to 
Kepler. No doubt the authorities of those days were even 
less willing to s]3end money on scientific matters than are 
the Governments of more recent times. For several years 
the imperial Treasury was importuned to relieve him 
from his anxieties. The effects of so much worry, and 
of the long journeys which were involved, at last broke 



down Kepler's health completely. As we have already 
mentioned, he had never been strong from infancy, and 
he finally succumbed to a fever in November, 1630, at the 
age of fifty-nine. He was interred at St. Peter's Church, 
at Ratisbon. 

Though Kepler had not those personal characteristics 
which have made his great predecessor, Tycho Brahe, 
such a romantic figure, yet a picturesque element in 
Kepler's character is not wanting. It was, however, of 
an intellectual kind. His imagination, as well as his 
reasoning faculties, always worked together. He was 
incessantly prompted by the most extraordinary specu- 
lations. The great majority of them were in a high 
degree wild and chimerical, but every now and then one 
of his fancies struck right to the heart of nature, and an 
immortal truth was brought to light. 

I remember visiting the observatory of one of our 
greatest modern astronomers, and in a large desk he 
showed me a multitude of photographs which he had 
attempted but which had not been successful, and then he 
showed me the few and rare pictures which had succeeded, 
and by which important truths had been revealed. With 
a felicity of expression which I have often since thought 
of, he alluded to the contents of the desk as the " chips." 
They were useless, but they were necessary incidents in 
the truly successful work. So it is in all great and good 
work. Even the most skilful man of science pursues 
many a wrong scent. Time after time he goes off on 
some track that plays him false. The greater the 
man's genius and intellectual resource, the more numerous 
will be the ventures which he makes, and the great 

KEPLER. lis 

majority of those ventures are certain to be fruitless. 
They are, in fact, the " chips/' In Kepler's case the 
chips were numerous enough. They were of the most 
extraordinary variety and structure. But every now and 
then a sublime discovery was made of such a character as 
to make us regard even the most fantastic of Kepler's 
chips with the greatest veneration and respect. 


It was just a year after the death of Galileo, that an infant 
came into the world who was christened Isaac Newton. 
Even the great fame of GaHleo himself must be relegated 
to a second place in comparison with that of the philo- 
sopher who first expounded the true theory of the 

Isaac Newton was born on the 25th of December (old 
style), 1642, at Woolsthorpe, in Lincolnshire, about a 
half-mile from Colsterworth, and eight miles south of 
Grantham. His father, Mr. Isaac Newton, had died a 
few months after his marriage to Harriet Ayscough, the 
daughter of Mr. James Ayscough, of Market Overton, in 
Eutlandshire. The little Isaac was at first so excessively 
frail and weakly that his life was despaired of. The 
watchful mother, however, tended her delicate child with 
such success that he seems to have thriven better than 
might have been expected from the circumstances of his 
infancy, and he ultimately acquired a frame strong enough 
to outlast the ordinary span of human life. 

For three years they continued to live at "Woolsthorpe, 
the widow's means of livelihood being supplemented by 
the income from another small estate at Sewstern, in a 
neighbouring part of Leicestershire. 



In 1645, Mrs. Newton took as a second husband the 
Rev. Barnabas Smith, and on moving to her new home, 
about a mile from Woolsthorpe, she entrusted little Isaac 
to her mother, Mrs. Ayscough. In due time we find that 
the boy was sent to the public school at Grantham, the 
name of the master being Stokes. For the purpose of 
being near his work, the embryo philosopher was boarded 
at the house of Mr. Clark, an apothecary at Grantham. 
"We learn from JSTewton himself that at first he had a 
very low place in the class lists of the school, and was 


"Woolsthorpe Manor. 
ShowDg solar dial made by Newton when a boy. 

by no means one of those model school-boys who find 
favour in the eyes of the school-master by attention to 
Latin grammar. Isaac's first incentive to diligent 
study seems to have been derived from the circumstance 
that he was severely kicked by one of the boys who was 
above him in the class. This indignity had the effect of 
stimulating young Newton's activity to such an extent 
that he not only attained the desired object of passing 
over the head of the boy who had maltreated him, but 
continued to rise until he became the head of the school. 


The play-hours of the great philosopher were devoted to 
pursuits very different from those of most school-boj^s. 
His chief amusement was found in making mechanical 
toys and various ingenious contrivances. He watched 
day by day with great interest the workmen engaged in 
constructing a windmill in the neighbourhood of the 
school, the result of which was that the boy made a work- 
ing model of the windmill and of its machinery, which 
seems to have been much admired, as indicating his apti- 
tude for mechanics. "We are told that Isaac also indulged 
in somewhat higher flights of mechanical enterprise. 
He constructed a carriage, the wheels of which were to 
be driven by the hands of the occupant, while the first 
philosophical instrument he made was a clock, which was 
actuated by water. He also devoted much attention to 
the construction of paper kites, and his skill in this respect 
was highly appreciated by his schoolfellows. Like a true 
philosopher, even at this stage he experimented on the 
best methods of attaching the string, and on the propor- 
tions which the tail ought to have. He also made Ian- 
thorns of paper to provide himself with light as he walked 
to school in the dark winter mornings. 

The only love affair in Newton's life appears to have 
commenced while he was still of tender years. The in- 
cidents are thus described in Brewster's " Life of !N^ew- 
ton," a work to which I am much indebted in this 

" In the house where he lodged there were some 
female inmates, in whose company he appears to have 
taken much pleasure. One of these, a Miss Storey, 
sister to Dr. Storey, a physician at Buckminster, near 


Colsterworth, was two or three years younger than New- 
ton, and to great personal attractions she seems to have 
added more than the usual allotment of female talent. 
The society of this young lady and her companions was 
always preferred to that of his own schoolfellows, and it 
was one of his most agreeable occupations to construct for 
them little tables and cupboards, and other utensils for 
holding their dolls and their trinkets. He had lived 
nearly six years in the same house with Miss Storey, and 
there is reason to believe that their youthful friendship 
gradually rose to a higher passion ; but the smallness 
of her portion, and the inadequacy of his own fortune, 
appear to have prevented the consummation of their 
happiness. Miss Storey was afterwards twice married, 
and under the name of Mrs, Yincent, Dr. Stukeley visited 
her at Grantham in 1727, at the age of eighty-two, and 
obtained from her many particulars respecting the early 
history of our author, l^ewton's esteem for her continued 
unabated during his life. He regularly visited her when 
he went to Lincolnshire, and never failed to relieve her 
from little pecuniary difficulties which seem to have beset 
her family." 

The schoolboy at Grantham was only fourteen years 
of age when his mother became a widow for the second 
time. She then returned to the old family home at 
Woolsthorpe, bringing with her the three children of her 
second marriage. Her means appear to have been some- 
what scanty, and it was consequently thought necessary 
to recall Isaac from the school. His recently-born in- 
dustry had been such that he had already made good pro- 
gress in his studies, and his mother hoped that he would 


now lay aside his books, and those silent meditations to 
which, even at this early age, he had become addicted. It 
was expected that, instead of such pursuits, which were 
deemed quite useless, the boy would enter busily into the 
duties of the farm and the details of a country life. But 
before long it became manifest that the study of nature 
and the pursuit of knowledge had such a fascination for 
the youth that he could give little attention to aught else. 
It was plain that he would make but an indifferent farmer. 
He greatly preferred experimenting on his water-wheels 
to looking after labourers, while he found that working 
at mathematics behind a hedge was much more interesting 
than chaffering about the price of bullocks in the market- 
place. Fortunately for humanity his mother, like a wise 
woman, determined to let her boy's genius have the scope 
which it required. He was accordingly sent back to 
Grrantham school, with the object of being trained in the 
knowledge which would fit him for entering the university 
of Cambridge. 

It was the 5th of June, 1660, when Isaac Newton, a 
youth of eighteen, was enrolled as an undergraduate of 
Trinity College, Cambridge. Little did those who sent 
him there dream that this boy was destined to be the 
most illustrious student who ever entered the portals of that 
great seat of learning. Little could the youth himself have 
foreseen that the rooms near the gateway which he occu- 
pied would acquire a celebrity from the fact that he dwelt 
in them, or that the ante- chapel of his college was in good 
time to be adorned by that noble statue, which is regarded 
as one of the chief art treasures of Cambridge University, 
both on account of its intrinsic beauty and the fact that 



Trinity College, Cambridge. 

Showing Newton's rooms ; on the leads of the gateway 
he placed his telescope. 

it commemorates the fame of her most distinguished alum- 
nus, Isaac Newton, the immortal astronomer. Indeed, 
his advent at the University seemed to have been by no 
means auspicious or brilliant. His birth was, as we have 
seen, comparatively obscure, and though he had already 
given indication of his capacity for reflecting on philoso- 
phical matters, yet he seems to have been but ill-equij)ped 
with the routine knowledge which youths are generally 
expected to take with them to the Universities. 

From the outset of his college career, Newton's atten- 


tion seems to have been mainly directed to mathematics. 
Here lie began to give evidence of that marvellous insight 
into the deep secrets of nature which more than a century 
later led so dispassionate a judge as Laplace to pronounce 
Newton's immortal work as pre-eminent above all the pro- 
ductions of the human intellect. But though Newton was 
one of the very greatest mathematicians that ever lived, 
he was never a mathematician for the mere sake of mathe- 
matics. He employed his mathematics as an instrument 
for discovering the laws of nature. His industry and 
genius soon brought him under the notice of the University 
authorities. It is stated in the University records that he 
obtained a Scholarship in 1664. Two years later we find 
that Newton, as well as many residents in the University, 
had to leave Cambridge temporarily on account of the 
breaking out of the plague. The philosopher retired for a 
season to his old home at Woolsthorpe, and there he 
remained until he was appointed a Pellow of Trinity 
College, Cambridge, in 1667. Prom this time onwards, 
Newton's reputation as a mathematician and as a natural 
philosopher steadily advanced, so that in 1669, while still 
but twenty-seven years of age, he was appointed to the dis- 
tinguished position of Lucasian Professor of Mathematics 
at Cambridge. Here he found the opportunity to continue 
and develop that marvellous career of discovery which 
formed his life's work. 

The earliest of Newton's great achievements in natural 
philosophy was his detection of the composite character of 
light. That a beam of ordinary sunlight is, in fact, a mix- 
ture of a very great number of different- coloured lights, 
is a doctrine now familiar to every one who has the 



slightest education in physical science. We must, how- 
ever, remember that this discovery was really a tremendous 
advance in knowledge at the time when Newton announced 

We here give the little diagram originally drawn by 


Newton, to explain the experiment by which he first 
learned the composition of light. A sunbeam is admitted 
into a darkened room through an opening, H, in a shutter. 
This beam when not interfered with will travel in a 
straight line to the screen, and there reproduce a bright 
spot of the same shape as the hole in the shutter. If, 
however, a prism of glass, A B C, be introduced so that 
the beam traverse it, then it will be seen at once that the 
light is deflected from its original track. There is, how- 
ever, a further and most important change which takes 
place. The spot of light is not alone removed to another 
part of the screen, but it becomes spread out into a long 
band beautifully coloured, and exhibiting the hues of the 
rainbow. At the top are the violet rays, and then in 
descending order we have the indigo, blue, green, yellow, 
orange, and red. 

The circumstance in this phenomenon which appears 


to have particularly arrested Newton's attention, was the 
elongation which the luminous spot underwent in conse- 
quence of its passage through the prism. When the 
prism was absent the spot was nearly circular, but when the 
prism was introduced the spot was about five times as long 
as it was broad. To ascertain the explanation of this was 
the first problem to be solved. It seemed natural to sup- 
pose that it might be due to the thickness of the glass in 
the prism which the light traversed, or to the angle of 
incidence at which the light fell upon the prism. He 
found, however, upon careful trial, that the phenomenon 
could not be thus accounted for. It was not until after 
much patient labour that the true explanation dawned 
upon him. He discovered that though the beam of white 
light looks so pure and so simple, yet in reality it is 
composed of differently coloured lights blended together. 
These are, of course, indistinguishable in the compound 
beam, but they are separated or disentangled, so to speak, 
by the action of the prism. The rays at the blue end of 
the spectrum are more powerfully deflected by the action 
of the glass than are the rays at the red end. Thus, the 
rays variously coloured red, orange, yellow, green, blue, 
indigo, violet, are each conducted to a different part of 
the screen. In this way the prism has the eiFect of 
exhibiting the constitution of the composite beam of light. 
To us this now seems quite obvious, but Newton did not 
adopt it hastily. With characteristic caution he verified 
the explanation by many different experiments, all of 
which confirmed his discovery. One of these may be 
mentioned. He made a hole in the screen at that part on 
which the violet rays fell. Thus a violet ray was allowed 


to pass tlirougli, all tlie rest of the light being intercepted, 
and on this beam so isolated he was able to try further 
experiments. For instance, when he interposed another 
prism in its path, he found, as he expected, that it was 
again deflected, and he measured the amount of the deflec- 
tion. Again he tried the same experiment with one of 
the red rays from the opposite end of the coloured band. 
He" allowed it to pass through the same aperture in the 
screen, and he tested the amount by which the second 
prism was capable of producing deflection. He thus found, 
as he had expected to find, that the second prism was 
more efficacious in bending the violet rays than in bending 
the red rays. Thus he confirmed the fact that the various 
hues of the rainbow were each bent by a prism to a dif- 
ferent extent, violet being acted upon the most, and red 
the least. 

Not only did !N^ewton decompose a white beam into its 
constituent colours, but conversely by interposing a second 
prism with its angle turned upwards, he reunited the 
diJSerent colours, and thus reproduced the original beam 
of white light. In several other ways also he illustrated 
his famous proposition, which then seemed so startling, 
that white light was the result of a mixture of all hues of 
the rainbow. By combining painters' colours in the 
proper proportion he did not indeed succeed in producing 
a mixture which would ordinarily be called white, but 
he obtained a grey pigment. Some of this he put on the 
floor of his room for comparison with a piece of white 
paper. He allowed a beam of bright sunlight to fall upon 
the paper and the mixed colours side by side, and a friend 
whom he called in for his opinion pronounced that under 



Isaac Newton. 

these circumstances tlie mixed colours looked the whiter 
of the two. 

By repeated demonstrations Kewton thus established 
his great discovery of the composite character of light. 
He at once perceived that his researches had an important 
bearing upon the principles involved in the construction 
of a telescope. Those who employed the telescope for look- 
ing at the stars, had been long aware of the imperfections 


which prevented all the various rays from being conducted 
to the same focus. But this imperfection had hitherto 
been erroneously accounted for. It had been supposed 
that the reason why success had not been attained in the 
construction of a refracting telescope was due to the fact 
that the object glass, made as it then was of a single 
piece, had not been properly shaped. Mathematicians 
had abundantly demonstrated that a single lens, if pro- 
perly figured, must conduct all rays of light to the same 
focus, provided all rays experienced equal refraction in 
passing through the glass. Until JN^ewton's discovery of 
the composition of white light, it had been taken for 
granted that the several rays in a white beam were 
equally refrangible. Ko doubt if this had been the case, 
a perfect telescope could have been produced by properly 
shaping the object glass. But when iS^ewton had demon- 
strated that light was by no means so simple as had been 
supposed, it became obvious that a satisfactory refracting 
telescope was an impossibility when only a single object 
lens was emplo3^ed, however carefully that lens might 
have been wrought. Such an objective might, no doubt, 
be made to conduct any one group of rays of a particular 
shade to the same focus, but the rays of other colours 
in the beam of white light must necessarily travel some- 
what astray. In this way Newton accounted for a great 
part of the difficulties which had hitherto beset the 
attempts to construct a perfect refracting telescope. 

We now know how these difficulties can be, to a great 
extent, overcome, by employing for the objective a com- 
posite lens made of two pieces of glass possessing different 
qualities. To these achromatic object glasses, as they 


are called, tlie great development of astronomical know- 
ledge, since Newton's time, is due. But it must be 
remarked that, although, the theoretical possibility of 
constructing an achromatic lens was investigated by New- 
ton, he certainly came to the conclusion that the difficulty 
could not be removed by employing a composite objective 
with two different kinds of glass. In this his marvellous 
sagacity in the interpretation of nature seems for once to 
have deserted him. "We can, however, hardly regret that 
Newton failed to discover the achromatic objective, when 
we observe that it was in consequence of his deeming an 
achromatic objective to be impossible that he was led to 
the invention of the reflecting telescope. Finding, as he 
believed, that the defects of the telescope could not be 
remedied by any application of the principle of refraction, 
he was led to look in quite a different direction for the 
improvement of the tool on which the advancement of 
astronomy depended. The refraction of light depended, 
as he had found, upon the colour of the light. The laws 
of reflection were, however, quite independent of the 
colour. Whether rays be red or green, blue or yellow, 
they are all reflected in precisely the same manner from a 
mirror. Accordingly, Newton perceived that if he could 
construct a telescope the action of which depended upon 
reflection, instead of upon refraction, the difficulty which 
had hitherto proved an insuperable obstacle to the im- 
provement of the instrument would be evaded. 

For this purpose Newton fashioned a concave mirror 
from a mixture of copper and tin, a combination which 
gives a surface with almost the lustre of silver. When the 
light of a star fell upon the surface, an image of the star 



Sir Isaac Newton's little Reflector. 

was produced in tlie focus of this mirror, and then this 
image was examined by a magnifying eye-piece. Such 
is the principle of the famous reflecting telescope which 
bears the name of I^ewton. The little reflector which he 
constructed, represented in the adjoining figure, is still 
preserved as one of the treasures of the E-oyal Society. 
The telescope tube had the very modest dimension of one 
inch in diameter. It was, however, the precursor of a 
whole series of magnificent instruments, each outstripping 
the other in magnitude, until at last the culminating point 
was attained in 1845, by the construction of Lord Eosse's 
mammoth reflector of six feet in aperture. 

Newton's discovery of the composition of light led to an 
embittered controversy, which caused no little worry to 
the great philosopher. Some of those who attacked him 
enjoyed considerable and, it must be admitted, even well- 
merited repute iii the ranks of science, They alleged^ 


however, that tlie elongation of the coloured band which 
Newton had noticed was due to this, to that, or to the 
other-— to anything, in fact, rather than to the true cause 
which Newton assigned. With characteristic patience and 
love of truth, Newton steadily replied to each such attack. 
He showed most completely how utterly his adversaries 
had misunderstood the subject, and how slight indeed was 
their acquaintance with the natural phenomenon in 
question. In reply to each point raised, he was ever 
able to cite fresh experiments and adduce fresh illustra- 
tions, until at last his opponents retired worsted from the 

It has been often a matter for surprise that Newton, 

throughout his whole career, should have taken so much 

trouble to expose the errors of those who attacked his 

views. He used even to do this when it plainly appeared 

that his adversaries did not understand the subject they 

were discussing. A philosopher might have said, " I 

know I am right, and whether others think I am right or 

not may be a matter of concern to them, but it is certainly 

not a matter about which I need trouble. If after having 

been told the truth they elect to remain in error, so much 

the worse for them ; my time can be better employed 

than in seeking to put such people right." This, however, 

was not Newton's method. He spent much valuable time 

in overthrowing objections which were often of a very 

futile description. Indeed, he suffered a great deal of 

annoyance from the persistency, and in some cases one 

might almost say from the rancour, of the attacks which 

were made upon him. Unfortunately for himself, he did 

not possess that capacity for sublime indifference to what 


men may say, whicli is often the happy possession of 
intellects greatly inferior to his. 

The subject of optics still continuing to engross 
Newton's attention, he followed up his researches into 
the structure of the sunbeam by many other valuable in- 
vestigations in connection with light. Every one has 
noticed the beautiful colours ma^nifested in a soap-bubble. 
Here was a subject which not unnaturally attracted the 
attention of one who had expounded the colours of the 
spectrum with such success. He perceived that similar 
hues were produced by other thin plates of transparent 
material besides soap-bubbles, and his ingenuity was suffi- 
cient to devise a method by which the thicknesses of the 
different films could be measured. "We can hardly, 
indeed, say that a like success attended his interpretation 
of these phenomena to that which had been so con- 
spicuous in his explanation of the spectrum. It implies 
no disparagement to the sublime genius of ISTewton to 
admit that the doctrines he put forth as to the causes of 
the colours in the soap-bubbles can be no longer accepted. 
"We must remember that Newton was a pioneer in account- 
ing for the physical properties of light. The facts that 
he established are indeed unquestionable, but the ex- 
planations which he was led to offer of some of them are 
seen to be untenable in the fuller light of our present 

Had Newton done nothing beyond making his wonder- 
ful discoveries in light, his fame would have gone down 
to posterity as one of the greatest of Nature's interpreters. 
But it was reserved for him to accomplish other dis- 
co veries^ which have pushed even his analysis of the 




•Ml \', 

Sir Isaac Newton's Sun-dial. 

sunbeam into tlie background ; it is lie who has expounded 
the system of the universe by the discovery of the law of 
universal gravitation. 

The age had indeed become ripe for the advent of the 
genius of Newton. Kepler had discovered with marvel- 
lous penetration the laws which govern the movements of 
the planets around the sun, and in various directions it 
had been more or less vaguely felt that the explanation of 


Kepler's laws, as well as of many other phenomena, must 
be sought for in connection with the attractive power of 
matter. But the mathematical analysis which alone could 
deal with this subject was wanting ; it had to be created 
by J^ewton. 

At Woolsthorpe, in the year 1666, Kewton's attention 
appears to have been concentrated upon the subject of 
gravitation. Whatever may be the extent to which we 
accept the more or less mythical story as to how the fall 
of an apple first directed the attention of the philosopher 
to the fact that gravitation must extend through space, it 
seems, at all events, certain that this is an excellent illus- 
tration of the line of reasoning which he followed. He 
argued in this way. The earth attracts the apple ; it 
would do so, no matter how high might be the tree from 
which that apple fell. It would then seem to follow that 
this power which resides in the earth by which it can 
draw all external bodies towards it, extends far beyond 
the altitude of the loftiest tree. Indeed, we seem to find 
no limit to it. At the greatest elevation that has ever 
been attained, the attractive power of the earth is still 
exerted, and though we cannot by any actual experiment 
reach an altitude more than a few miles above the earth, 
yet it is certain that gravitation would extend to eleva- 
tions far greater. It is plain, thought J^ewton, that an 
apple let fall from a point a hundred miles above this 
earth's surface, would be drawn down by the attraction, 
and would continually gather fresh velocity until it 
reached the ground. From a hundred miles it was natural 
to think of what would happen at a thousand miles, or 
at hundreds of thousands of miles. JN^o doubt the intensity 


of the attraction becomes weaker with every increase in 
the altitude, but that action would still exist to sorae ex- 
tent, however lofty might be the elevation which had been 

It then occurred to Newton, that though the moon is 
at a distance of two hundred and forty thousand miles 
from the earth, yet the attractive power of the earth 
must extend to the moon. He was particularly led to 
think of the moon in this connection, not only because the 
moon is so much closer to the earth than are any of the 
other celestial bodies, but also because the moon is an 
appendage to the earth, always revolving around it. The 
moon is certainly attracted to the earth, and yet the moon 
does not fall down; how is this to be accounted for? 
The explanation was to be found in the character of the 
moon's present motion. If the moon were left for a 
moment at rest, there can be no doubt that the attraction 
of the earth would begin to draw the lunar globe in 
towards our globe. In the course of a few days our 
satellite would come down on the earth with a most fear- 
ful crash. This catastrophe is averted by the circum- 
stance that the moon has a movement of revolution around 
the earth. Newton was able to calculate from the known 
laws of mechanics, which he had himself been mainly 
instrumental in discovering, what the attractive power of 
the earth must be, so that the moon shall move precisely 
as we find it to move. It then appeared that the very 
power which makes an apple fall at the earth's surface, 
is the power which guides the moon in its orbit. 

Once this step had been taken, the whole scheme ol 
the universe might almost be said to have become unrolled 



before the eye o£ the philosopher. It was natural to sup- 
pose that just as the moon was guided and controlled by the 
attraction of the earth, so the earth itself, in the course of 
its great annual progress, should be guided and controlled 
by the supreme attractive power of the sun. If this were 
so with regard to the earth, then it would be impossible to 
doubt that in the same way the movements of the planets 

Sir Isaac Newton's Telescope. 

could be explained to be cohsequences of solar attraction. 
It was at this point that the great laws of Kepler became 
especially significant. Kepler had shown how each of 
the planets revolves in an ellipse around the sun, which is 
situated on one of the foci. This discovery had been 
arrived at from the interpretation of observations. Kepler 
had himself assigned no reason why the orbit of a planet 
should be an ellipse rather than any other of the infinite 
number of closed curves which might be traced around the 
sun. Kepler had also shown, and here again he was 
merely deducing the results from observation, that when 
the movements of two planets were compared together, 
the squares of the periodic times in which each planet 


revolved were proportional to the cubes of their mean 
distances from the sun. This also Kepler merely knew to 
be true as a fact, he gave no demonstration of the reason 
why nature should have adopted this particular relation 
between the distance and the periodic time rather than 
any other. Then, too, there was the law by which Kepler, 
with unparalleled ingenuity, explained the way in which 
the velocity of a planet varies at the different points of its 
track, when he showed how the line drawn from the sun to 
the planet described equal areas around the sun in equal 
times. These were the materials with which JN^ewton set 
to work. He proposed to infer from these the actual 
laws regulating the force by which the sun guides the 
planets. Here it was that his sublime mathematical 
genius came into play. Step by step Newton advanced 
until he had completely accounted for all the phenomena. 

In the first place, he showed that as the planet describes 
equal areas in equal times about the sun, the attractive 
force which the sun exerts upon it must necessarily be 
directed in a straight line towards the sun itself. He 
also demonstrated the converse truth, that whatever be 
the nature of the force which emanated from a sun, yet so 
long as that force was directed through the sun's centre, 
any body which revolved around it must describe equal 
areas in equal times, and this it must do, whatever be the 
actual character of the law according to which the inten- 
sity of the force varies at different parts of the planet's 
journey. Thus the first advance was taken in the exposi- 
tion of the scheme of the universe. 

The next step was to determine the law according to 
which the force thus proved to reside in the sun varied 


with the distance of the planet. Newton presently showed 
by a most superb effort of mathematical reasoning, that if 
the orbit of a planet were an ellipse and if the sun were 
at one of the foci of that ellipse, the intensity of the 
attractive force must vary inversely as the square of the 
planet's distance. If the law had any other expression 
than the inverse square of the distance, then the orbit 
which the planet must follow would not be an ellipse ; or 
if an ellipse, it would, at all events, not have the sun in 
the focus. Hence he was able to show from Kepler's laws 
alone that the force which guided the planets was an 
attractive power emanating from the sun, and that the 
intensity of this attractive power varied with the inverse 
square of the distance between the two bodies. 

These circumstances being known, it was then easy to 
show that the last of Kepler's three laws must necessarily 
follow. If a number of planets were revolving around 
the sun, then supposing the materials of all these bodies 
were equally affected by gravitation, it can be demon- 
strated that the square of the periodic time in which each 
planet completes its orbit is proportional to the cube of 
the greatest diameter in that orbit. 

These superb discoveries were, however, but the starting- 
point from which l^ewton entered on a series of researches, 
which disclosed many of the profoundest secrets in the 
scheme of celestial mechanics. His natural insight 
showed that not only large masses like the sun and the 
earth, and the moon, attract each other, but that every 
particle in the universe must attract every other particle 
with a force which varies inversely as the square of the dis- 
tance between them. If, for example, the two particles 



Sir Isaac Newton's Astrolabe. 

were placed twice as far apart, tlien tlie intensity of the 
force whicli souglit to bring them, together would be re- 
duced to one-fourth. If two particles, originally ten miles 
asunder, attracted each other with a certain force, then, 
when the distance was reduced to one mile, the intensity 
of the attraction between the two particles would be 
increased one-hundred-fold. This fertile principle extends 


throughout the whole of nature. In some cases, however, 
the calculation of its effect upon the actual problems o£ 
nature would be hardly possible, were it not for another 
discovery which JN^ewton's genius enabled him to accom- 
plish. In the case of two globes like the earth and the 
moon, we must remember that we are dealing not with 
particles, but with two [mighty masses of matter, each 
composed of innumerable myriads of particles. Every 
particle in the earth does attract every particle in the 
moon with a force which varies inversely as the square of 
their distance. The calculation of such attractions is 
rendered feasible by the following principle. Assuming 
that the earth consists of materials symmetrically ar- 
ranged in shells of varying densities, we may then, in 
calculating its attraction, regard the whole mass of the 
globe as concentrated at its centre. Similarly we may 
regard the moon as concentrated at the centre of its mass. 
In this way the earth and the moon can both be regarded 
as particles in point of size, each particle having, however, 
the entire mass of the corresponding globe. The attrac- 
tion of one particle for another is a much more simple 
matter to investigate than the attraction of the myriad 
different points of the earth upon the myriad different 
points of the moon. 

Many great discoveries now crowded in upon Kewton. 
He first of all gave the explanation of the tides that ebb 
and flow around our shores. Even in the earliest times 
the tides had been shown to be related to the moon. It 
was noticed that the tides were specially high during full 
moon or during new moon, and this circumstance obviously 
pointed to the existence of some connection between the 


moon and these movements of the water, though as to 
what that connection was no one had any accurate con- 
ception until JN^ewton announced the law of gravitation. 
Newton then made it plain that the rise and fall of the 
water was simply a consequence of the attractive power 
which the moon exerted upon the oceans lying upon our 
globe. He showed also that to a certain extent the sun 
produces tides, and he was able to explain how it was 
that when the sun and the moon both conspire, the joint 
result was to produce especially high tides, which we call 
" spring tides " ; whereas if the solar tide was low, while 
the lunar tide was high, then we had the phenomenon of 
" neap " tides. 

But perhaps the most signal of N^ewton's applications 
of the law of gravitation was connected with certain 
irregularities in the movements of the moon. In its orbit 
round the earth our satellite is, of course, mainly guided 
by the great attraction of our globe. If there were no 
other body in the universe, then the centre of the moon 
must necessarily perform an ellipse, and the centre of the 
earth would lie in the focus of that ellipse. Nature, 
however, does not allow the movements to possess the 
simplicity which this arrangement would imply, for the 
sun is present as a source of disturbance. The sun attracts 
the moon, and the sun attracts the earth, but in different 
degrees, and the consequence is that the moon's move- 
ment with regard to the earth is seriously affected by the 
influence of the sun. It is not allowed to move exactly 
in an ellipse, nor is the earth exactly in the focus. How 
great was Newton's achievement in the solution of this 
problem will be appreciated if we realise that he not only 


had to determine from the law of gravitation the nature 
of the disturbance of the moon, but he had actually to 
construct the mathematical tools by which alone such 
calculations could be effected. 

The resources of Newton's genius seemed, however, to 
prove equal to almost any demand that could be made 
upon it. He saw that each planet must disturb the other, 
and in that way he was able to render a satisfactory 
account of certain phenomena which had perplexed all 
preceding investigators. That mysterious movement by 
which the pole of the earth sways about among the stars 
had been long an unsolved enigma, but Newton showed 
that the moon grasped with its attraction the protuberant 
mass at the equatorial regions of the earth, and thus 
tilted the earth's axis in a way that accounted for the 
phenomenon which had been known but had never been 
explained for two thousand years. All these discoveries 
were brought together in that immortal work, Newton's 
** Principia." 

Down to the year 1687, when the ''Principia" was 
published, Newton had lived the life of a recluse at 
Cambridge, being entirely occupied "vvith those transcen- 
dent researches to which we have referred. But in 
that year he issued from his seclusion under circum- 
stances of considerable historical interest. King James 
the Second attempted an invasion of the rights and 
privileges of the University of Cambridge by issuing a 
command that Father Francis, a Benedictine monk, should 
be received as a Master of Arts in the University, without 
having taken the oaths of allegiance and supremacy. 
With this arbitrary comm^-nd the University sternly 


refused to comply. The Yice-Chancellor was accordingly 
summoned to answer for an act of contempt to tlie authority 
of the Crown. Newton was one of nine delegates who 
were chosen to defend the independence of the University 
before the High Court. They were able to show that 
Charles the Second, who had issued a mandamus under 
somewhat similar circumstances, had been induced after 
due consideration to withdraw it. This argument appeared 
satisfactory, and the University gained their case. New- 
ton's next step in public life was his election, by a narrow 
majority, as member for the University, and during the 
years 1688 and 1689, he seems to have attended to his 
parliamentary duties with considerable regularity. 

An incident which happened in 1692 was apparently 
the cause of considerable disturbance in Newton's equani- 
mity, if not in his health. He had gone to early morning 
chapel, leaving a lighted candle among his papers on his 
desk. Tradition asserts that his little dog " Diamond " 
upset the candle ; at all events, when Newton came back 
he found that many valuable papers had perished in a 
conflagration. The loss of these manuscripts seems to 
have had a serious effect. Indeed, it has been asserted 
that the distress reduced Newton to a state of mental 
aberration for a considerable time. This has, apparently, 
not been confirmed, but there is no doubt that he experi- 
enced considerable disquiet, for in writing on September 
13th, 1693, to Mr. Pepys, he says : 

" I am extremely troubled at the embroilment I am in, 
and have neither ate nor slept well this twelvemonth, nor 
have my former consistency of mind." 

Notwithstanding the fame which Newton had achieved 
by the publication of his "Principia,'' and by all his 


researclies, the State had not as yet taken any notice 
whatever of the most illustrious man of science that this 
or any other country has ever produced. Many of his 
friends had exerted themselves to procure him some 
permanent appointment, but without success. It happened, 
however, that Mr. Montagu, who had sat with Newton in 
Parliament, was appointed Chancellor of the Exchequer 
in 1694. Ambitious of distinction in his new office, Mr. 
Montagu addressed himself to the improvement of the 
current coin, which was then in a very debased condition. 
It fortunately happened that an opportunity occurred of 
appointing a new official in the Mint ; and Mr. Montagu 
on the 19th of March, 1695, wrote to offer Mr. Newton 
the position of warden. The salary was to be ^'^q or six 
hundred a year, and the business would not require more 
attendance than Newton could spare. The Lucasian 
professor accepted this post, and forthwith entered upon 
his new duties. 

The knowledge of physics which Newton had acquired 
by his experiments was of much use in connection with 
his duties at the Mint. He carried out the re-coinage 
with great skill in the course of two years, and as a reward 
for his exertions, he was appointed, in 1697, to the Master- 
ship of the Mint, with a salary between £1,200 and 
£1,500 per annum. In 1701 his duties at the Mint being 
so engrossing, he resigned his Lucasian professorship at 
Cambridge, and at the same time he had to surrender his 
fellowship at Trinity College. This closed his connection 
with the University of Cambridge. It should, however, 
be remarked that at a somewhat earlier stage in his career 
he was very nearly being appointed to an office which 
might have enabled the University to retain the great 


philosopher within its precincts. Some of his friends 
had almost succeeded in securing his nomination to the 
Provostship of King's College, Cambridge ; the appoint- 
ment, however, fell through, inasmuch as the statute 
could not be evaded, which required that the Provost of 
King's College should be in holy orders. 

In those days it was often the custom for illustrious 
mathematicians, when they had discovered a solution for 
some new and striking problem, to publish that problem 
as a challenge to the world, while withholding their own 
solution. A famous instance of this is found in what is 
known as the Brachistochrone problem, which was solved 
by John Bernouilli. The nature of this problem may be 
mentioned. It was to find the shape of the curve along 
which a body would slide down from one point (a) to 
another point (b) in the shortest time. It might at first 
be thought that the straight line from A to b, as it is 
undoubtedly the shortest distance between the points, 
would also be the path of quickest descent ; but this is 
not so. There is a curved line, down which a bead, let us 
^ay, would run on a smooth wire from a to b in a shorter 
time than the same bead would require to run down the 
straight wire. Bernouilli' s problem was to find out what 
that curve must be. Newton solved it correctly; he 
showed that the curve was a part of what is termed a 
cycloid — that is to say, a curve like that which is des- 
cribed by a point on the rim of a carriage-wheel as the 
wheel runs along the ground. Such was Newton's geo- 
metrical insight that he was able to transmit a solution of 
the problem on the day after he had received it, to the 
President of the Eoyal Society. 

In 1703 Newton, whose world-wide fame was now 


established, was elected President of the Royal Society. 
Year after year lie was re-elected to this distinguished 
position, and his tenure, which lasted twenty-five years, 
only terminated with his life. It was in discharge of his 
duties as President of the Eoyal Society that Newton was 
brought into contact with Prince George of Denmark. 
In April, 1705, the Queen paid a visit to Cambridge as 
the guest of Dr. Bentley, the then Master of Trinity, and 
in a court held at Trinity Lodge on April 15th, 1705, the 
honour of knighthood was conferred upon the discoverer 
of gravitation. 

Urged by illustrious friends, who sought the promotion 
of knowledge, Newton gave his attention to the publica- 
tion of a new edition of the "Principia." His duties at 
the Mint, however, added to the supreme duty of carry- 
ing on his original investigations, left him but little time 
for the more ordinary task of the revision. He was 
accordingly induced to associate with himself for this 
purpose a distinguished young mathematician, Hoger 
Coates, a Fellow of Trinity College, Cambridge, who had 
recently been appointed Plumian Professor of Astronomy. 
On July 27th, 1713, Newton, by this time a favourite at 
Court, waited on the Queen, and presented her with a copy 
of the new edition of the " Principia.'^ 

Throughout his life Newton appears to have been 
greatly interested in theological studies, and he specially 
devoted his attention to the subject of prophecy. He 
left behind him a manuscript on the prophecies of Daniel 
and the Apocalypse of St. John, and he also wrote vari- 
ous theological papers. Many other subjects had from 
time to time engaged his attention. He studied the laws 



of heat ; lie experimented in pursuit of tlie dreams of the 
Alchymist ; while the philosopher who had revealed the 
mechanism of the heavens found occasional relaxation in 
trying to interpret hieroglyphics. In the last few years 
of his life he bore with fortitude a painful ailment, and 
on Monday, March 20th, 1727, he died in the eighty-fifth 
year of his age. On Tuesday, March 28th, he was buried 
in Westminster Abbey. 

Though Newton lived long enough to receive the honour 
that his astonishing discoveries so justly merited, and 
though for many years of his life his renown was much 
greater than that of any of his contemporaries, yet it is 
not too much to say that, in the years which have since 
elapsed, Newton's fame has been ever steadily advancing, 
so that it never stood higher than it does at this moment. 

"We .hardly know whether to admire more the sublime 
discoveries at which he arrived, or the extraordinary 
character of the intellectual processes by which those dis- 
coveries were reached. Yiewed from either standpoint, 
Newton's *' Principia " is incomparably the greatest work 
on science that has ever yet been produced. . 

Sir Isaac Newton's Sun-dial in the Eoyal Society. 


Among the manuscripts preserved at GreenwicL. Observa- 
tory are certain documents in which Flamsteed gives an 
account of his own life. We may commence our sketch 
by quoting the following passage from this autobiography : 
— " To keep myself from idleness, and to recreate myself, 
I have intended here to give some account of my life, in 
my youth, before the actions thereof, and the providences 
of God therein, be too far passed out of my memory ; and 
to observe the accidents of all my years, and inclinations 
of my mind, that whosoever may light upon these papers 
may see I was not so wholly taken up, either with my 
father's business or my mathematics, but that I both 
admitted and found time for other as weighty considera- 

The chief interest which attaches to the name of 
Flamsteed arises from the fact that he was the first of the 
illustrious series of Astronomers Eoyal who have presided 
over Greenwich Observatory. In that capacity Flam- 
steed was able to render material assistance to Newton by 
providing him with the observations which his lunar 
theory required. 

John Flamsteed was born at Denby, in Derbyshire, on 


the loth, of August, 1646. His motlier died when, he was 
three years old, and the second wife, whom his father 
took three years later, only lived until Flamsteed was 
eight, there being also two younger sisters. In his 
boyhood the future astronomer tells us that he was very 
fond of those romances which affect boy's imagination, 
but as he writes, "At twelve years of age I left all the 
wild ones and betook myself to read the better sort of 
them, which, though they were not probable, yet carried 
no seeming impossibility in the picturing." By the time 
Flamsteed was fifteen years old he had embarked in still 
more serious work, for he had read Plutarch's " Lives," 
Tacitus' " Eoman History," and many other books of a 
similar description. In 1661 he became ill with some 
serious rheumatic affection, which obliged him to be 
withdrawn from school. It was then for the first time 
that he received the rudiments of a scientific education. 
He had, however, attained his sixteenth year before he 
made any progress in arithmetic. He tells us how 
his father taught him "the doctrine of fractions," and 
" the golden rule of three " — lessons which he seemed to 
have learned easily and quickly. One of the books which 
he read at this time directed his attention to astronomical 
instruments, and he was thus led to construct for himself 
a quadrant, by which he could take some simple astro- 
nomical observations. He further calculated a table to 
give the sun's altitudes at diff'erent hours, and thus dis- 
played those tastes for practical astronomy which he 
lived to develop so greatly. It appears that these scien- 
tific studies were discountenanced by his father, who 
designed that his son should follow a business career. 


Flamsteed's natural inclination, however, forced him to 
prosecute astronomical work, notwithstanding the im- 
pediments that lay in his path. Unfortunately, his con- 
stitutional delicacy seems to have increased, and he had 
just completed his eighteenth year, " when," to use his 
own words, "the winter came on and thrust me again 
into the chimney, whence the heat and the dryness of the 
preceding summer had happily once before withdrawn me. 
But, it not being a fit season for physic, it was thought 
fit to let me alone this winter, and try the skill of another 
physician on me in the spring.'* 

It appears that at this time a quack, named Valentine 
Greatrackes, was reputed to have effected most astonishing 
cures in Ireland merely by the stroke of his hands, with- 
out the application of any medicine whatever. Flam- 
steed's father, despairing of any remedy for his son from 
the legitimate branch of the profession, despatched him 
to Ireland on August 26th, 1665, he being then, as 
recorded with astronomical accuracy, *^ nineteen years, six 
days, and eleven hours old." The young astronomer, 
accompanied by a friend, arrived on a Tuesday at Liver- 
pool, but the wind not being favourable, they remained 
there till the following Friday, when a shift of the wind to 
the east took place. They embarked accordingly on a 
vessel called the Supply at noon, and on Saturday night 
came in sight of Dublin. Ere they could land, however, 
they were nearly being wrecked on Lambay Island. 
This peril safely passed, there was a long delay for quaran- 
tine before they were at last allowed on shore. On Thurs- 
day, September 6th, they set out from Dublin, where 
they had been sojourning at the *'Ship" Hotel, in Dame 


Street, towards Assaune, where Greatrackes received his 

riamsteed gives an interesting account of his travels 
in Ireland. They dined at [N^aas on the first day, and on 
September 8th they reached Carlow, a town which is 
described as one of the fairest they saw on their journey. 
By Sunday morning; September 10th, having lost their 
way several times, they reached Castleton, called com- 
monly Four Mile Waters. Flamsteed inquired of the 
host in the inn where they might find a church, but 
was told that the minister lived twelve miles away, and 
that they had no sermon except when he came to 
receive his tithes once a year, and a woman added that, 
" they had plenty enough of everything necessary except 
the word of God." The travellers accordingly went on 
to Cappoquin, which lies up the river Blackwater, on the 
road to Lismore, eight miles from Youghal. Thence 
they immediately started on foot to Assaune, about a 
mile from Cappoquin, and entering into the house of 
Mr. Greatrackes, they saw him touch several patients, 
''whereof some were nearly cured, others were on the 
mending hand, and some on whom his strokes had no 
effect." Flamsteed was touched by the famous quack 
on the afternoon of September 11th, but we are hardly 
surprised to hear his remark that " he found not his 
disease to stir." Next morning the astronomer came 
again to see Mr. Greatrackes, who had "a kind of 
majestical yet affable presence, and a composed carriage." 
Even after the third touching had been submitted to, no 
benefit seems to have been derived. We must, however, 
record, to the credit of Mr. Greatrackes, that he refused to 







riamsteed's House. 

accept any payment from Flamsteecl, because he was a 

Finding it useless to protract his stay any longer, 
Flamsteed and his friend set out on their return to Dublin. 
In the course of his journey he seems to have been much 
impressed with Clonmel, which he describes as an *' exceed- 
ingly pleasantly seated town." But in those days a jour- 
ney to Ireland was so serious an enterprise that when 
Flamsteed did arrive safely back at Derby after an ab- 
sence of a month, he adds, ''For God's providence in this 
journey. His name be praised. Amen." 

As to the expected benefits to his health from the 
expedition we may quote his own words : "In the winter 
following I was indifferent hearty, and my disease was 
not so violent as it used to be at that time formerly. But 
whether through God's mercy I received this through Mr. 


Greatrackes' toucli, or my journey and vomiting at sea, I 
am uncertain ; but, by some circumstances, I guess that I 
received a benefit from botb." 

It is evident tbat by this time Flamsteed's interest 
in all astronomical matters bad greatly increased. He 
studied the construction of sun-dials, be formed a cata- 
logue of seventy of tbe fixed stars, with tbeir places on 
tbe beavens, and be computed tbe circumstances of tbe 
solar eclipse wbicb was to bappen on June 22nd, 
1666. It is interesting to note tbat even in tbose days 
tbe doctrines of tbe astrologers still found a considerable 
degree of credence, and Flam steed spent a good deal of bis 
time in astrological studies and computations. He investi- 
gated tbe metbods of casting a nativity, but a suspicion, or, 
indeed, ratber more tban a suspicion, seems to bave crossed 
bis mind as to tbe value of tbese astrological predictions, 
for be says in fine, " I found astrology to give generally 
strong conjectural bints, not perfect declarations." 

All tbis time, bowever, tbe future Astronomer Eoyal 
was steadily advancing in astronomical inquiries of a 
recondite nature. He bad investigated tbe obliquity of 
tbe ecliptic witb extreme care, so far as tbe circum- 
stances of astronomical observation would at tbat time 
permit. He bad also sougbt to discover tbe sun's dis- 
tance from tbe eartb in so far as it could be obtained by 
determining wben tbe moon was exactly balf illuminated, 
and be bad measured, witb mucb accuracy, tbe lengtb of 
tbe tropical year. It will tbus be seen tbat, even at tbe 
age of twenty, Flamsteed bad made marked progress, con- 
sidering bow mucb bis time bad been interfered witb by 


Other branches of astronomy began also to claim his 
attention. We learn that in 1669 and 1670 he compared 
the planets Jupiter and Mars with certain fixed stars near 
which they passed. His instrumental means, though very 
imperfect, were still sufficient to enable him to measure 
the intervals on the celestial sphere between the planets 
and the stars. As the places of the stars were known, 
Flamsteed was thus able to obtain the places of the 
planets. This is substantially the way in which astro- 
nomers of the present day still proceed when they desire 
to determine the places of the planets, inasmuch as, 
directly or indirectly, those places are always obtained 
relatively to the fixed stars. By his observations at this 
early period, Flamsteed was, it is true, not able to obtain 
any very great degree of accuracy ; he succeeded, however, 
in proving that the tables by which the places of the 
planets were ordinarily given were not to be relied upon. 

Flamsteed's labours in astronomy and in the allied 
branches of science were now becoming generally known, 
and he gradually came to correspond with many dis- 
tinguished men of learning. One of the first occasions 
which brought the talents of the young astronomer into 
fame was the publication of some calculations concerning 
certain astronomical phenomena which were to happen in 
the year 1670. In the monthly revolution of the moon 
its disc passes over those stars which lie along its track. 
The disappearance of a star by the interposition of the 
moon is called an " occultation." Owing to the fact that 
our satellite is comparatively near us, the position which 
the moon appears to occupy on the heavens varies from 
different parts of the earth. It consequently happens 


that a star whicli would be occulted to an observer in one 
locality, would often not be occulted to an observer who was 
situated elsewbere. Even when an occultation is visible 
from both places, the times at which the star disappears 
from view will, generally speaking, be different. Much 
calculation is therefore necessary to decide the circum- 
stances under which the occultations of stars may be 
visible from any particular station. Having a taste for 
such computations, Flamsteed calculated the occultations 
which were to happen in the year 1670, it being the case 
that several remarkable stars would be passed over by the 
moon during this year. Of course at the present time 
we find such information duly set forth in the Nautical 
Almanac, but a couple of centuries ago there was no 
such source of astronomical knowledge as is now to be 
found in that invaluable publication, which astronomers 
and navigators know so well. Flamsteed accordingly 
sent the results of his work to the President of the 
Boyal Society. The paper which contained them was 
received very favourably, and at once brought Flamsteed 
into notice among the most eminent members of that 
illustrious body, one of whom, Mr. Collins, became 
through life his faithful friend and constant correspon- 
dent. Flamsteed' s father was naturally gratified with 
the remarkable notice which his son was receiving from 
the great and learned ; accordingly he desired him 
to go to London, that he might make the personal ac- 
quaintance of those scientific friends whom he had only 
known by correspondence previously. Flamsteed was 
indeed glad to avail himself of this opportunity. Thus 
he became acquainted with Dr. Barrow, and especially 



li 1 

with Newton, who was then Lucasian Professor of Mathe- 
matics at Cambridge. It seems to have been in conse- 
quence of this visit to London that Flamsteed entered 
himself as a member of Jesus College, Cambridge. We 
have but little information as to his University career, 
but at all events he took his degree of M.A. on June 5th, 

Up to this time it would seem that Flamsteed had been 
engaged, to a certain extent, in the business carried on by 


his father. It is true that he does not give any explicit 
details, yet there are frequent references to journeys 
which he had to take on business matters. But the time 
now approached when Flamsteed was to start on an 
independent career, and it appears that he took his degree 
in Cambridge with the object of entering into holy orders, 
so that he might settle in a small living near Derby, which 
was in the gift of a friend of his father, and would be at 
the disposal of the young astronomer. This scheme was, 
however, not carried out, but Flamsteed does not tell us 
why it failed, his only remark being, that " the good pro- 
vidence of God that had designed me for another station 
ordered it otherwise.'* 

Sir Jonas Moore, one of the influential friends whom 
Flamsteed' s talents had attracted, seems to have procured 
for him the position of king's astronomer, with a salary of 
£100 per annum. A larger salary appears to have been 
designed at first for this office, which was now being 
newly created, but as Flamsteed was resolved on taking 
holy orders, a lesser salary was in his case deemed suffi- 
cient. The building of the observatory, in which the first 
Astronomer Eoyal was to be installed, seems to have been 
brought about, or, at all events, its progress was ac- 
celerated, in a somewhat curious manner. 

A Frenchman, named Le Sieur de S. Pierre, came over 
to London to promulgate a scheme for discovering longi- 
tudes, then a question of much importance. He brought 
with him introductions to distinguished people, and his 
mission attracted a great deal of attention. The proposals 
which he made came under Flamsteed's notice, who 
pointed out that the Frenchman's projects were quite 


inapplicable in the present state of astronomical science, 
inasmuch as the places of the stars were not known with 
the degree of accuracy which would be necessary if such 
methods were to be rendered available. Plamsteed then 
goes on to say : — " I heard no more of the Frenchman 
after this ; but was told that my letters had been shown 
King Charles. He was startled at the assertion of the 
fixed stars' places being false in the catalogue, and said, 
with some vehemence, he must have them anew observed, 
examined, and corrected, for the use of his seamen. '* 

The first question to be settled was the site for the new 
observatory. Hyde Park and Chelsea College were both 
mentioned as suitable localities, but, at Sir Christopher 
"Wren's suggestion, Greenwich Hill was finally resolved 
upon. The king made a grant of five hundred pounds of 
money. He gave bricks from Tilbury Fort, while 
materials, in the shape of wood, iron, and lead, were 
available from a gatehouse demolished in the Tower. 
The king also promised whatever further material aid 
might be shown to be necessary. The first stone of the 
Boyal Observatory was laid on August 10th, 1675, and 
within a few years a building was erected in which 
the art of modern practical astronomy was to be created. 
Flamsteed strove with extraordinary diligence, and in 
spite of many difficulties, to obtain a due provision of 
astronomical instruments, and to arrange for the carrying 
on of his observations. JN^otwithstanding the king's pro- 
mises, the astronomer was, however, but scantily provided 
with means, and he had no assistants to help him in his 
work. It follows that all the observations, as well as the 
reductions, and, indeed, all the incidental work of the 


observatory, liad to be carried on by himself alone. Flam- 
steed, as we have seen, bad, bowever, many staunch 
friends. Sir Jonas Moore in particular at all times ren- 
dered him most valuable assistance, and encouraged him 
by the warm sympathy and keen interest which he showed 
in astronomy. The work of the first Astronomer Royal 
was frequently interrupted by recurrent attacks of the 
complaints to which we have already referred. He says 
himself that '* his distempers stick so close that he cannot 
remove them,'' and he lost much time by prostration from 
headaches, as well as from more serious affections. 

The year 1678 found him in the full tide of work in 
his observatory. He was specially engaged on the pro- 
blem of the earth's motion, which he sought to derive 
from observations of the sun and of Venus. But this, as 
well as many other astronomical researches which he 
undertook, were only subsidiary to that which he made 
the main task of his life, namely, the formation of a cata- 
logue of fixed stars. At the time when Flamsteed com- 
menced his career, the only available catalogue of fixed 
stars was that of Tycho Brahe. This work had been 
published at the commencement of the seventeenth cen- 
tury, and it contained about a thousand stars. The posi- 
tions assigned to these stars, though obtained with won- 
derful skill, considering the many difficulties under which 
Tycho laboured, were quite inaccurate when judged 
by our modern standards. Tycho's instruments were 
necessarily most rudely divided, and he had, of course, no 
telescopes to aid him. Consequently it was merely by a 
process of sighting that he could obtain the places of the 
stars. It must further be remembered that Tycho had 


no clocks, and no micrometers. He had, indeed, but little 
correct knowledge of tlie motions of the heavenly bodies 
to guide him. To determine the longitudes of a few 
principal stars he conceived the ingenious idea of 
measuring by day the position of Yenus with respect 
to the sun, an observation which the exceptional bright- 
ness of this planet rendered possible without telescopic 
aid, and then by night he observed the position of 
Yenus with regard to the stars. 

It has been well remarked by Mr. Baily, in his intro- 
duction to the " British Catalogue of Stars,'' that "Flam- 
steed's observations, by a fortunate combination of cir- 
cumstances, commenced a new and a brilliant era. It 
happened that, at that period, the powerful mind of 
Newton was directed to this subject ; a friendly inter- 
course then existed between these two distinguished 
characters ; and thus the first observations that could lay 
any claim to accuracy were at once brought in aid of 
those deep researches in which our illustrious geometer 
was then engaged. The first edition of the ' Principia ' 
bears testimony to the assistance afforded by Flamsteed to 
Newton in these inquiries ; although the former considers 
that the acknowledgment is not so ample as it ought to 
have been." 

Although Flamsteed' s observations can hardly be said 
to possess the accuracy of those made in more recent 
times, when instruments so much superior to his have 
been available, yet they possess an interest of a special 
kind from their very antiquity. This circumstance 
renders them of particular importance to the astronomer, 
inasmuch as they are calculated to throw light on the 


proper motions of the stars. Flamsteed's work may, 
indeed, be regarded as the origin of all subsequent cata- 
logues, and the nomenclature which he adopted, though 
in some respects it can hardly be said to be very defen- 
sible, is, nevertheless, that which has been adopted by all 
subsequent astronomers. There were also a great many 
errors, as might be expected in a work of such extent, 
composed almost entirely of numerical detail. Many of 
these errors have been corrected by Baily himself, the as- 
siduous editor of "Flamsteed's Life and Works," for Flam- 
steed was so harassed from various causes in the latter 
part of his life, and was so subject to infirmities all 
through his career, that he was unable to revise his com- 
putations with the care that would have been necessary. 
Indeed, he observed many additional stars which he never 
included in the British Catalogue. It is, as Baily well 
remarks, " rather a matter of astonishment that he ac- 
complished so much, considering his slender means, his 
weak frame, and the vexations which he constantly 

Flamsteed had the misfortune, in the latter part of his 
life, to become estranged from his most eminent scientific 
contemporaries. He had supplied JSTewton with places of 
the moon, at the urgent solicitation of the author of the 
" Principia," in order that the lunar theory should be 
carefully compared with observation. But Flamsteed 
appears to have thought that in Newton's further request 
for similar information, he appeared to be demanding as 
a right that which Flamsteed considered he was only 
called upon to render as a favour. A considerable dispute 
grew out of this matter, and there are many letters and 


documents, bearing on the difficulties which subsequently 
arose, that are not, perhaps, very creditable to either 

Notwithstanding his feeble constitution, Flamsteed 
lived to the age of seventy -three, his death occurring on 
the last day of the year 1719. 



Isaac Newton was just fourteen years of age wlien tlie 
birth, of Edmund Halley, who was destined in after years 
to become Newton's warmly attached friend, and one of 
his most illustrious scientific contemporaries, took place. 
There can be little doubt that the fame as an astronomer 
which Halley ultimately acquired, great as it certainly 
was, would have been even greater still had it not been 
somewhat impaired by the misfortune that he had to shine 
in the same sky as that which, was illumined by the un- 
paralleled genius of Newton. 

Edmund Halley was born at Haggerston, in th.e Parish, 
of St. Leonard's, Shoreditch, on October 29th, 1656. His 
father, who bore the same name as his famous son, was a 
soap-boiler in Winchester Street, London, and he had 
conducted his business with such success that he accumu- 
lated an ample fortune. I have been unable to obtain 
more than a very few particulars with respect to the early 
life of the future astronomer. It would, however, appear 
that from boyhood he showed considerable aptitude for 
the acquisition of various kinds of learning, and he also 
had some capacity for mechanical invention. Halley 

H ALLEY. 163 

seems to have received a sound education at St. Paul's 
School, then under the care of Dr. Thomas Gale. 

Here the young philosopher rapidly distanced his com- 
petitors in the various branches of ordinary school instruc- 
tion. His superiority was, however, most conspicuous in 
mathematical studies, and, as a natural development of 
such tastes, we learn that by the time he had left school 
he had already made good progress in astronomy. At 
the age of seventeen he was entered as a commoner at 
Queen's College, Oxford, and the reputation that he 
brought with him to the University may be inferred from 
the remark of the writer of " Atheneo Oxonienses," that 
*' Halley came to Oxford with skill in Latin, Greek, and 
Hebrew, and such a knowledge of geometry as to make a 
complete dial." Though his studies were thus of a some- 
what multifarious nature, yet it is plain that from the 
first his most favourite pursuit was astronomy. His ear- 
liest efforts in practical observation were connected with 
an eclipse which he observed from his father's house in 
Winchester Street. It also appears that he had studied 
theoretical branches of astronomy so far as to be conver- 
sant with the application of mathematics to somewhat 
abstruse problems. 

Up to the time of Kepler, philosophers had assumed 
almost as an axiom that the heavenly bodies must revolve 
in circles, and that the motion of the planet around the 
orbit which it described must be uniform. We have 
already seen how that great philosopher, after very per- 
severing labour, succeeded in proving that the orbits of 
the planets were not circles, but that they were ellipses 
of small eccentricity. Kepler was, however, unable to 


shake himself free from the prevailing notion that the 
angular motion of the planet ought to be of an uniform 
character around some point. He had indeed proved that 
the motion round the focus of the ellipse in which the 
sun lies is not of this description. One of his most 
important discoveries even related to the fact that at 
some parts of its orbit a planet swings around the sun 
with greater angular velocity than at others. But it so 
happens that in elliptic tracks which differ but little from 
circles, as is the case with all the more important plane- 
tary orbits, the motion round the empty focus of the 
ellipse is very nearly uniform. It seemed natural to 
assume, that this was exactly the case, in which event 
each of the two foci of the ellipse would have had a 
special significance in relation to the movement of the 
planet. The youthful Halley, however, demonstrated 
that so far as the empty focus was concerned, the move- 
ment of the planet around it, though so nearly uniform, 
was still not exactly so, and at the age of nineteen, he 
published a treatise on the subject which at once placed 
him in the foremost rank amongst theoretical astro- 

But Halley had no intention of being merely an astro- 
nomer with his pen. He longed to engage in the prac- 
tical work of observing. He saw that the progress of 
exact astronomy must depend largely on the determina- 
tion of the positions of the stars with all attainable accu- 
racy. He accordingly determined to take up this branch 
of work, which had been so successfully initiated by 
Tycho Brahe. 

At the present day, astronomers of the great national 

H ALLEY. 165 

observatories are assiduously engaged in the determina- 
tion of the places of the stars. A knowledge of the exact 
positions of these bodies is indeed of the most fundamental 
importance, not alone for the purposes of scientific astro- 
nomy, but also for navigation and for extensive operations 
of surveying in which accuracy is desired. The fact that 
Halley determined to concentrate himself on this work 
shows clearly the scientific acumen of the young astro- 

Halley, however, found that Hevelius, at Dantzig, and 
Flamsteed, the Astronomer Eoyal at Greenwich, were 
both engaged on work of this character. He accordingly 
determined to direct his energies in a way that he thought 
would be more useful to science. He resigned to the two 
astronomers whom I have named the investigation of the 
stars in the northern hemisphere, and he sought for him- 
self a field hitherto almost entirely unworked. He deter- 
mined to go to the southern hemisphere, there to measure 
and survey those stars which were invisible in Europe, so 
that his work should supj)lement the labours of the 
northern astronomers, and that the joint result of his 
labours and of theirs might be a complete survey of the 
most important stars on the surface of the heavens. 

In these days, after so many ardent students every- 
where have devoted themselves to the study of Nature, it 
seems difficult for a beginner to find a virgin territory in 
which to commence his explorations. Halley may, how- 
ever, be said to have enjoyed the privilege of commencing 
to work in a magnificent region, the contents of which 
were previously almost entirely unknown. Indeed none 
of the stars which were so situated as to have been 


invisible from Tyclio Brahe's observatory at TJraniborg, in 
Denmark, could be said to have been properly observed. 
There was, no doubt, a rumour that a Dutchman had ob- 
served southern stars from the island of Sumatra, and 
certain stars were indicated in the southern heavens on a 
celestial globe. On examination, however, Halley found 
that no reliance could be placed on the results which had 
been obtained, so that practically the field before him may 
be said to have been unworked. 

At the age of twenty, without having even waited to 
take that degree at the university which the authorities 
would have been glad to confer on so promising an 
undergraduate, this ardent student of Nature sought his 
father's permission to go to the southern hemisphere for 
the purpose of si adying the stars which lie around the 
southern pole. His father possessed the necessary means, 
and he had likewise the sagacity to encourage the young 
astronomer. He was indeed most anxious to make every- 
thing as easy as possible for so hopeful a son. He pro- 
vided him with an allowance of £300 a year, which was 
regarded as a very munificent provision in those days. 
Halley was also furnished with letters of recommendation 
from King Charles II., as well as from the directors of 
the East India Company. He accordingly set sail with 
his instruments in the year 1676, in one of the East 
India Company's ships, for the island of St. Helena, which 
he had selected as the scene of his labours. 

After an uneventful voyage of three months, the 
astronomer landed on St. Helena, with his sextant of 
5i feet radius, and a telescope 24 feet long, and forthwith 
plunged with ardour into his investigation of the southern 




skies. He met, however, with one very considerable dis- 
appointment. The climate of this island had been repre- 
sented to him as most favourable for astronomical obser- 
vation ; but instead of the pure blue skies he had been 
led to expect, he found that they were almost always 
more or less clouded, and that rain was frequent, so that 
his observations were very much interrupted. On this 
account he only remained at St. Helena for a single 
year, having, during that time, and in spite of many diffi- 


culties, accompKslied a piece of work whicli earned for 
him the title of " our southern Tycho." Thus did Halley 
establish his fame as an astronomer on the same lonely 
rock in mid- Atlantic, which nearly a century and a-half 
later became the scene of J^apoleon's imprisonment, when 
his star, in which he believed so firmly, had irretrievably 

On his return to England, Halley prepared a map 
which showed the result of his labours, and he presented 
it to the king, in 1677. Like his great predecessor 
Tycho, Halley did not altogether disdain the arts of the 
courtier, for he endeavoured to squeeze a new constellation 
into the group around the southern pole which he styled 
" The E-oyal Oak,'' adding a description to the effect that 
the incidents of which " The Eoyal Oak " was a symbol 
were of sufficient importance to be inscribed on the surface 
of the heavens. 

There is reason to think that Charles II. duly appre- 
ciated the scientific renown which one of his subjects had 
achieved, and it was probably through the influence of 
the king that Halley was made a Master of Arts at 
Oxford on November 18th, 1678. Special reference was 
made on the occasion to his observations at St. Helena, as 
evidence of unusual attainments in mathematics and as- 
tronomy. This degree was no small honour to such a 
young man, who, as we have seen, quitted his university 
before he had the opportunity of graduating in the 
ordinary manner. 

On November 30th, in the same year, the astronomer 
received a further distinction in being elected a Fellow of 
the Royal Society. From this time forward he took a 

H ALLEY. 169 

most active part in the affairs of the Society, and the 
numerous papers which he read before it form a very 
valuable part of that notable series of volumes known as 
the *^ Philosophical Transactions.'' He was subsequently 
elected to the important office of secretary to the E-oyal 
Society, and he discharged the duties of his post until his 
appointment to Greenwich necessitated his resignation. 

Within a year of Halley's election as a Fellow of the 
E,oyal Society, he was chosen by the Society to represent 
them in a discussion which had arisen with Hevelius. 
The nature of this discussion, or rather the fact that any 
discussion should have been necessary, may seem strange 
to modern astronomers, for the point is one on which it 
would now seem impossible for there to be any difference 
of opinion. We must, however, remember that the days 
of Halley were, comparatively speaking, the days of 
infancy as regards the art of astronomical observation, and 
issues that now seem obvious were often, in those early 
times, the occasions of grave and anxious consideration. 
The particular question on which Halley had to represent 
the Royal Society may be simply stated. When Tycho 
Brahe made his memorable investigations into the places 
of the stars, he had no telescopes to help him. The 
famous instruments at IJraniborg were merely provided 
with sights, by which the telescope was pointed to a star 
on the same principle as a rifle is sighted for a target. 
Shortly after Tycho' s time, Galileo invented the telescojoe. 
Of course every one admitted at once the extraordinary 
advantages which the telescope had to offer, so far as the 
mere question of the visibility of objects was concerned. 
But the bearing of Galileo's invention upon what we 


may describe as the measuring part of astronomy was 
not so immediately obvious. If a star be visible to tbe 
unaided eye, we can determine its place by such, instru- 
ments as those which Tycho used, in which no telescope 
is employed. "We can, however, also avail ourselves of 
an instrument in which we view the star not directly but 
through the intervention of the telescope. Can the place 
of the star be determined more accurately by the latter 
method than it can when the telescope is dispensed with ? 
"With our present knowledge, of course, there is no doubt 
about the answer ; every one conversant with instruments 
knows that we can determine the place of a star far more 
accurately with the telescope than is possible by any 
mere sighting apparatus. In fact an observer would be 
as likely to make an error of a minute with the sighting 
apparatus in Tycho' s instrument, as he would be to make 
an eri^or of a second with the modern telescope, or, to 
express the matter somewhat di:fferently, we maj^ say, 
speaking quite generally, that the telescopic method of 
determining the places of the stars does not lead to 
errors more than one- sixtieth part as great as the errors 
which are unavoidable when we make use of Tycho' s 

But though this is so apparent to the modern astrono- 
mer, it was not at all apparent in the days of Halley, and 
accordingly he was sent off to discuss the question with 
the Continental astronomers. Hevelius, as the representa- 
tive of the older method, which Tycho had employed with 
such success, maintained that an instrument could be 
pointed more accurately at a star by the use of sights 
than by the use of a telescope, and vigorously disputed 

H ALLEY. 171 

the claims put forward by those who believed that the 
latter method was the more suitable. On May 14th, 1679, 
Halley started for Dantzig, and the energetic character of 
the man may be judged from the fact that on the very 
night of his arrival he commenced to make the necessary 
observations. In those days astronomical telescopes had 
only obtained a fractional part of the perfection possessed 
by the instruments in our modern observatories, and 
therefore it may not be surprising that the results of the 
trial were not immediately conclusive. Halley appears to 
have devoted much time to the investigation ; indeed, he 
remained at Dantzig for more than a twelvemonth. On 
his return to England, he spoke highly of the skill which 
Hevelius exhibited in the use of his antiquated methods, 
but Halley was nevertheless too sagacious an observer to 
be shaken in his preference for the telescopic method of 

The next year we find our young astronomer starting 
for a Continental tour, and we, w^ho complain if the 
Channel passage lasts more than an hour or two, may 
note Halley 's remark in writing to Hooke on June 15th, 
1680: ''Having fallen in with bad weather we took 
forty hours in the journey from Dover to Calais." The 
scientific distinction which he had already attained was 
such that he was received in Paris with marked attention. 
A great deal of his time seems to have been passed in the 
Paris observatory, where Cassini, the presiding genius, 
himself an astronomer of well- deserved repute, had 
extended a hearty welcome to his English visitor. They 
made observations together of the place of the splendid 
comet which was then attracting universal attention, and 


Halley found the work thus done of much use when he 
subsequently came to investigate the path pursued by this 
body. Halley was wise enough to spare no pains to derive 
all possible advantages from his intercourse with the dis- 
tinguished savants of the French capital. In the further 
progress of his tour he visited the principal cities of the 
Continent, leaving behind him everywhere the memory of 
an amiable disposition and of a rare intelligence. 

After Halley's return to England, in 1682, he married 
a young lady named Mary Tooke, with whom he lived 
happily, till her death fifty-five years later. On his 
marriage, he took up his abode in Islington, where he 
erected his instruments and recommenced his observa- 

It has often been the good fortune of astronomers to 
render practical services to humanity by their investiga- 
tions, and Halley' s achievements in this respect deserve to 
be noted. A few years after he had settled in England, 
he published an important paper on the variation of the 
magnetic compass, for so the departure of the needle from 
the true north is termed. This subject had indeed early 
engaged his attention, and he continued to feel much 
interest in it up to the end of his life. With respect to 
his labours in this direction. Sir John Herschel says : 
*' To Halley we owe the first appreciation of the real com- 
plexity of the subject of magnetism. It is wonderful 
indeed, and a striking proof of the penetration and saga- 
city of this extraordinary man, that with his means of 
information he should have been able to draw such con- 
clusions, and to take so large and comprehensive a view of 
the subject as he appears to have done." In 1692, Halley 

H ALLEY. 173 

explained Ms theory of terrestrial magnetism, and begged 
captains of sliips to take observations of the variations of 
the compass in all parts of the world, and to communicate 
them to the Royal Society, " in order that all the facts 
may be readily available to those who are hereafter to 
complete this difficult and complicated subject/* 

The extent to which Halley was in advance of his con- 
temporaries, in the study of terrestrial magnetism, may be 
judged from the fact that the subject was scarcely touched 
after his time till the year 1811. The interest which he 
felt in it was not of a merely theoretical kind, nor was it 
one which could be cultivated in an easy-chair. Like all 
true investigators, he longed to submit his theory to the 
test of experiment, and for that purpose Halley deter- 
mined to observe the magnetic variation for himself. He 
procured from King William III. the command of a vessel 
called the Paramour Fink, with which he started for the 
South Seas in 1694. This particular enterprise was 
not, however, successful ; for, on crossing the line, some 
of his men fell sick and one of his lieutenants mutinied, 
so that he was obliged to return the following year with 
his mission unaccomplished. The government cashiered 
the lieutenant, and Halley having procured a second 
smaller vessel to accompany the Paramour Pink, started 
once more in September, 1699. He traversed the Atlantic 
to the 52nd degree of southern latitude, beyond which his 
further advance was stopped. " In these latitudes," he 
writes to say, " we fell in with great islands of ice of so 
incredible height and magnitude, that I scarce dare write 
my thoughts of it." 

On his return in 1700, Halley published a general 


chart, showing the variation of the compass at the dif- 
ferent places which he had visited. On these charts he 
set down lines connecting those localities at which the 
magnetic variation was identical. He thus set an example 
of the graphic representation of large masses of complex 
facts, in such a manner as to appeal at once to the eye, a 
method of which we make many applications in the 
present day. 

Eut probably the greatest service which Halley ever 
rendered to human knowledge was the share which he 
took in bringing Newton's "Principia " before the world. 
In fact, as Dr. Glaisher, writing in 1888, has truly re- 
marked, " but for Halley the 'Principia ' would not have 

It was a visit from Halley in the year 1684 which 
seems to have first suggested to Newton the idea of pub- 
lishing the results of his investigations on gravitation. 
Halley, and other scientific contemporaries, had no 
doubt some faint glimmering of the great truth which 
only Newton's genius was able fully to reveal. Halley 
had indeed shown how, on the assumptions that the planets 
move in circular orbits round the sun, and that the 
squares of their periodic times are proportional to the cubes 
of their mean distances, it may be proved that the force 
acting on each planet must vary inversely as the square 
of its distance from the sun. Since, however, each of the 
planets actually moves in an ellipse, and therefore, at con- 
tinually varying distances from the sun, it becomes a 
much more difficult matter to account mathematically for 
the body's motions on the supposition that the attractive 
force varies inversely as the square of the distance. This 

HALLEY, 175 

was the question with which Halley found himself con- 
fronted, but which his mathematical abilities were not 
adequate to solve. It would seem that both Hooke and Sir 
Christopher Wren were interested in the same problem ; 
in fact, the former claimed to have arrived at a solution, 
but declined to make known his results, giving as an 
excuse his desire that others having tried and failed 
might learn to value his achievements all the more. 
Halley, however, confessed that his attempts at the solu- 
tion were unsuccessful, and "Wren, in order to encourage 
the other two philosophers to pursue the inquiry, offered 
to present a book of forty shillings' value to either of them 
who should in the space of two months bring him a 
convincing proof of it. Such was the value which Sir 
Christopher set on the Law of Gravitation, upon which 
the whole fabric of modern astronomy may be said to 

Finding himself unequal to the task, Hallej^ went 
down to Cambridge to see J^ewton on the subject, and was 
delighted to learn that the great mathematician had 
already completed the investigation. He showed Halley 
that the motions of all the planets could be completely 
accounted for on the hypothesis of a force of attraction 
directed towards the sun, which varies inversely as the 
square of the distance from that body. 

Halley had the genius to perceive the tremendous im- 
portance of Newton's researches, and he ceased not to 
urge upon the recluse man of science the necessity 
for giving his new discoveries publication. He paid 
another visit to Cambridge with the object of learning 
more with regard to the mathematical methods which 


had already conducted JSTewton to sucIl sublime truths, 
and lie again encouraged the latter both to pursue his 
investigations, and to give some account of them to the 
world. In December of the same year Halley had the 
gratification of announcing to the Royal Society that 
]N^ewton had promised to send that body a paper contain- 
ing his researches on Gravitation. 

It seems that at this epoch the finances of the Royal 
Society were at a very low ebb. This impecuniosity was 
due to the fact that a book by Willoughby, entitled 
**De Historia Piscium,'* had been recently printed by the 
society at great expense. In fact, the coffers were so low 
that they had some difficulty in paying the salaries of 
their permanent officials. It appears that the public did 
not care about the history of fishes, or at all events the 
volume did not meet with the ready demand which was 
expected for it. Indeed, it has been recorded that when 
Halley had undertaken to measure the length of a degree 
of the earth's surface, at the request of the Royal Society, 
it was ordered that his expenses be defrayed either in 
£50 sterling, or in fifty books of fishes. Thus it happened 
that on June 2nd, the Council, after due consideration 
of ways and means in connection with the issue of the 
" Principia,'* ordered that Halley " should undertake the 
business of looking after the book and printing it at 
his own charge," which he engaged to do. 

It was, as we have elsewhere mentioned, characteristic 
of Newton that he detested controversies, and he was, in 
fact, inclined to suppress the third book of the ^'Principia" 
altogether rather than have any conflict with Hooke with 
respect to the discoveries there enunciated. He also thought 

H ALLEY. 177 

of changing the name of the work to Be Motu Corporum 
Librl Duo, but upon second thoughts, he retained the 
original title, remarking, as he wrote to Halley, " It will 
help the sale of the book, which I ought not to diminish, 
now it is yours," a sentence which shows conclusively, if 
further proof were necessary, that Halley had assumed 
the responsibility of its publication. 

Halley spared no pains in pushing forward the publi- 
cation of his illustrious friend's great work, so that in 
the same year he was in a position to present a com- 
plete copy to King James II., with a proper discourse of 
his own. Halley also wrote a set of Latin hexameters 
in praise of !N'ewtoii's genius, which he printed at the 
beginning of the work. The last line of this specimen of 
Halley 's poetic muse may be thus rendered : '' Nor 
mortals nearer may approach the gods." 

The intimate friendship between the two greatest 
astronomers of the time continued without interruption 
till the death of Newton. It has, indeed, been alles-ed 
that some serious cause of estrangement arose between 
them. There is, however, no satisfactory ground for this 
statement ; indeed, it may be regarded as effectually dis- 
posed of by the fact that, in the year 1727, Halley took up 
the defence of his friend, and wrote two learned papers in 
support of Newton's ^' System of Chronology," which had 
been seriously attacked by a certain ecclesiastic. It is 
quite evident to any one who has studied these papers 
that Halley's friendship for Newton was as ardent as 

The generous zeal with which Halley adopted and 
defended the doctrines of Newton with regard to t^Q 


movements of the celestial bodies was presently rewarded 
by a brilliant discovery, wbich has more than any of bis 
otber researches rendered, bis name a familiar one to 
astronomers. Newton, having explained the movements 
of the planets, was naturally led to turn his attention to 
comets. He perceived that their journey ings could be 
completely accounted for as consequences of the attrac- 
tion of the sun, and he laid down the principles by which 
the orbit of a comet could be determined, provided that 
observations of its positions were obtained at three dif- 
ferent dates. The importance of these principles was by no 
one more quickly recognised than by Halley, who saw at 
once that it provided the means of detecting something 
like order in the movements of these strange wanderers. 
The doctrine of Gravitation seemed to show that just as 
the planets revolved around the sun in ellipses, so also 
must the comets. The orbit, however, in the case of a 
comet, is so extremely elongated that the very small part 
of the elliptic path within which the comet is both near 
enough and bright enough to be seen from the earth, is 
indistinguishable from a parabola. Applying these prin- 
ciples, Halley thought it would be instructive to study 
the movements of certain bright comets, concerning 
which reliable observations could be obtained. At the 
expense of much labour, he laid down the paths pursued 
by twenty-four of these bodies, which had appeared 
between the years 1337 and 1698. Amongst them he 
noticed three, which followed tracks so closely resem- 
bling each other, that he was led to conclude the so- 
called three comets could only have been three different 
appearances of the same body. The first of these occurred 

HALLEY, 179 

in 1531, tlie second was seen by Kepler in 1607, and tlie 
third by Halley himself in 1682. These dates suggested 
that the observed phenomena might be due to the succes- 
sive returns of one and the same comet after intervals 
of seventy-five or seventy-six years. On the further 
examination of ancient records, Halley found that a 
comet had been seen in the year 1456, a date, it will be 
observed, seventy-five years before 1531. Another had 
been observed seventy-six years earlier than 1456, viz., in 
1380, and another seventy-five years before that, in 1305. 

As Halley thus found that a comet had been recorded 
on several occasions at intervals of seventy-five or seventy- 
six years, he was led to the conclusion that these several 
apparitions related to one and the same object, which was 
an obedient vassal of the sun, performing an eccentric 
journey round that luminary in a period of seventy-five 
or seventy-six years. To realise the importance of this 
discovery, it should be remembered that before Halley*s 
time a comet, if not regarded merely as a sign of divine 
displeasure, or as an omen of intending disaster, had at 
least been regarded as a chance visitor to the solar system, 
arriving no one knew whence, and going no one knew 

A supreme test remained to be applied to Halley's 
theory. The question arose as to the date at which this 
comet would be seen again. "We must observe that the 
question was complicated by the fact that the body, in 
the course of its voyage around the sun, was exposed 
to the incessant disturbing action produced by the 
attraction of the several planets. The comet, there- 
fore, does not describe a simple ellipse as it would 


do if the attraction of the sun were the only force 
by which its movement were controlled. Each of the 
planets solicits the comet^ to depart from its track, and 
though the amount of these attractions may be insignifi- 
cant in comparison with the supreme controlling force of the 
sun, yet the departure from the ellipse is quite sufficient 
to produce appreciable irregularities in the comet's move- 
ment. At the time when Halley lived, no means existed 
of calculating with precision the eflPect of the disturbance 
a comet might experience from the action of the different 
planets. Halley exhibited his usual astronomical sagacity 
in deciding that Jupiter would retard the return of the 
comet to some extent. Had it not been for this disturb- 
ance the comet would apparently have been due in 1757 
or early in 1758. But the attraction of the great planet 
would cause delay, so that Halley assigned, for the date 
of its re-appearance, either the end of 1758 or the begin- 
ning of 1759. Halley knew that he could not himself live 
to witness the fulfilment of his prediction, but he says : 
"If it should return, according to our predictions, about 
the year 1758, impartial posterity will not refuse to 
acknowledge that this was first discovered by an English- 
man." This was, indeed, a remarkable prediction of 
an event to occur fifty- three years after it had been uttered. 
The way in which it was fulfilled forms one of the most 
striking episodes in the history of astronomy. The comet 
was first seen on Christmas Day, 1758, and passed through 
its nearest point to the sun on March 13th, 1759. Halley 
had then been lying in his grave for seventeen years, yet the 
verification of his prophecy reflects a glory on his name, 
which will cause it to live for eyer in the annals of 

H ALLEY. i8i 

astronomy. The comet paid a subsequent visit in 1835, 
and its next appearance is due about 1910. 

Halley next entered upon a labour wbicb, if less strik- 
ing to the imagination than his discoveries with regard to 
comets, is still of inestimable value in astronomy. He 
undertook a series of investigations with the object of 
improving our knowledge of the movements of the planets. 
This task was practically finished in 1719, though the 
results of it were not published until after his death in 
1749. In the course^of it he was led to investigate closely 
the motion of Venus, and thus he came to recognise for 
the first time the peculiar importance which attaches to 
the phenomenon of the transit of this planet across the 
sun. Halley saw that the transit, which was to take 
place in the year 1761, would afford a favourable oppor- 
tunity for determining the distance of the sun, and thus 
learning the scale of the solar system. He predicted the 
circumstances of the phenomenon with an astonishing 
degree of accuracy, considering his means of information, 
and it is unquestionably to the exertions of Halley in 
urging the importance of the matter upon astronomers 
that we owe the unexampled degree of interest taken in 
the event, and the energy which scientific men exhibited 
in observing it. The illustrious astronomer had no hope 
of being himself a witness of the event, for it could not 
happen till many years after his death. This did not, 
however, diminish his anxiety to impress upon those who 
would then be alive, the importance of the occurrence, nor 
did it lead him to neglect anything which might contri- 
bute to the success of the observations. As we now know, 
Halley rather over-estimated the value of the transit of 


Venus, as a means of determining the solar distance. 
The fact is that the circumstances are such that the 
observation of the time of contact between the edge of 
the planet and the edge of the sun cannot be made with 
the accuracy which he had expected. 

In 1691, Halley became a candidate for the Savilian 
Professorship of Astronomy at Oxford. He was not, 
however, successful, for his candidature was opposed by 
Flamsteed, the Astronomer Hoyal of the time, and 
another was appointed. He received some consolation 
for this particular disappointment by the fact that, in 
1696, owing to Newton's friendly influence, he was 
appointed deputy Controller of the Mint at Chester, an 
office which he did not retain for long, as it was abolished 
two years later. At last, in 1703, he received what he 
had before vainly sought, and he was appointed to the 
Savilian chair. 

His observations of the eclipse of the sun, which 
occurred in 1715, added greatly to Halley's reputation. 
This phenomenon excited special attention, inasmuch as it 
was the first total eclipse of the sun which had been 
visible in London since the year 1140. Halley under- 
took the necessary calculations, and predicted the various 
circumstances with a far higher degree of precision than 
the official announcement. He himself observed the 
phenomenon from the Eoyal Society's rooms, and he 
minutely describes the outer atmosphere of the sun, now 
known as the corona ; without, however, offering an 
opinion as to whether it was a solar or a lunar appendage. 

At last Halley was called to the dignified office which 
he of all men was most competent to fill. On February 

H ALLEY. 183 

9tli, 1720, lie was appointed Astronomer Eoyal in succes- 
sion to Flamsteed. He found things at the Boyal 
Observatory in a most unsatisfactory state. Indeed, 
there were no instruments, nor anything else that was 
movable ; for such things, being the property of Flam- 
steed, had been removed by his widow, and though Halley 
attempted to purchase from that lady some of the instru- 
ments which his predecessor had employed, the unhappy 
personal differences which had existed between him and 
Flamsteed, and which, as we have already seen, prevented 
his election as Savilian Professor of Astronomy, proved a 
bar to the negotiation. Greenwich Observatory wore a 
very different appearance in those days, from that which 
the modern visitor, who is fortunate enough to gain admis- 
sion, may now behold. Not only did Halley find it bereft 
of instruments, we learn besides that he had no assistants, 
and was obliged to transact the whole business of the 
establishment single-handed. 

In 1721, however, he obtained a grant of £500 from 
the Board of Ordnance, and accordingly a transit instru- 
ment was erected in the same year. Some time afterwards 
he procured an eight-foot quadrant, and with these instru- 
ments, at the age of sixty-four, he commenced a series of 
observations on the moon. He intended, if his life was 
spared, to continue his observations for a period of eigh- 
teen years, this being, as astronomers know, a very 
important cycle in connection with lunar movements. 
The special object of this vast undertaking was to improve 
the theory of the moon's motion, so that it might serve 
more accurately to determine longitudes at sea. This 
self-imposed task Halley lived to carry to a successful 


termination, and the tables deduced from his observations, 
and published after his death, were adopted almost 
universally by astronomers, those of the French nation 
being the only exception. 

Throughout his life Halley had been singularly free 
from illness of every kind, but in 1737 he had a stroke of 
paralysis. Notwithstanding this, however, he worked 
diligently at his telescope till 1739, after which his health 
began rapidly to give way. He died on January 14th, 
1742, in the eighty-sixth year of his age, retaining his 
mental faculties to the end. He was buried in the 
cemetery of the church of Lee in Kent, in the same grave 
as his wife, who had died five years previously. We are 
informed by Admiral Smyth that Pond, a later Astrono- 
mer Koyal, was afterwards laid in the same tomb. 

Halley's dispos-ition seems to have been generous and 
candid, and wholly free from anything like jealousy or 
rancour. In person he was rather above the middle 
height, and slight in build ; his complexion was fair, and 
he is said to have always spoken, as well as acted, with un- 
common sprightliness. In the eloge pronounced upon him at 
the VQ.-ns> Academie des Sciences, of which Halley had been 
made a member in 1719, it was said, "'he possessed all 
the qualifications which were necessary to please princes 
who were desirous of instruction, with a great extent of 
knowledge and a constant presence of mind ; his answers 
were ready, and at the same time pertinent, judicious, 
polite and sincere." 

Thus we find that Peter the Great was one of his most 
ardent admirers. He consulted the astronomer on matters 
connected with shipbuilding', and invited him to his own 



table. But Halley possessed nobler qualifications tban the 
capacity of pleasing princes. He was able to excite and 
to retain tbe love and admiration of his equals. Tbis was 
due to tbe warmtb of bis attachments, tbe unselfishness 
of bis devotion to bis friends, and to a vein of gaiety and 
good-humour which pervaded all his conversation. 


James Bradley was descended from an ancient family 
in the county of Durham. He was born in 1692 or 1693, 
at Shetbourne, in Gloucestershire, and was educated in 
the Grammar School at Northleach. From thence he 
proceeded in due course to Oxford, where he was admitted 
a commoner at Balliol College, on March 15th, 1711. 
Much of his time, while an undergraduate, was passed 
in Essex with his maternal uncle, the Eev. James Pound, 
who was a well-known man of science and a diligent 
observer of the stars. It was doubtless by intercourse 
with his uncle that young Bradley became so expert in 
the use of astronomical instruments, but the immortal 
discoveries he subsequently made show him to have been 
a born astronomer. 

The first exhibition of Bradley's practical skill seems to 
be contained in two observations which he made in 1717 
and 1718. They have been published by Halley, whose 
acuteness had led him to perceive the extraordinary 
scientific talents of the young astronomer. Another illus- 
tration of the sagacity which Bradley manifested, even at 
the very commencement of his astronomical career, is 


contained in a remark of Halley's, who says : '^Dr. Pound 
and his nephew, Mr. Bradley, did, myself being present, 
in the last opposition of the sun and Mars this way de- 
monstrate the extreme minuteness of the sun's parallax, 
and that it was not more than twelve seconds nor less 
than nine seconds." To make the significance of this plain, 
it should be observed that the determination of the sun's 
parallax is equivalent to the determination of the dis- 
tance from the earth to the sun. At the time of which 
we are now writing, this very important unit of celestial 
measurement was only very imperfectly known, and the 
observations of Pound and Bradley may be interpreted 
to mean that, from their observations, they had come to 
the conclusion that the distance from the earth to the 
sun must be more than 94 millions of miles, and less 
than 125 millions. "We now, of course, know that they 
were not exactly right, for the true distance of the sun 
is about 93 millions of miles. We oannot, however, but 
think that it was a very remarkable approach for the 
veteran astronomer and his brilliant nephew to make 
towards the determination of a magnitude which did not 
become accurately known till fifty years later. 

Among the earliest parts of astronomical work to which 
Bradley's attention was directed, were the eclipses of 
Jupiter's satellites. These phenomena are specially 
attractive inasmuch as they can be so readily observed^ 
and Bradley found it extremely interesting to calculate 
the times at which the eclipses should take place, and then 
to compare his observations with the predicted times. 
From the success that he met with in this work, and from 
his other labours, Bradley's reputation as an astronomer 


increased so greatly that on JSTovember tlie 6th, 1718, he 
was elected a Fellow of the Boyal Society. 

Up to this time the astronomical investigations of 
Bradley had been more those of an amateur than of a pro- 
fessional astronomer, and as it did not at first seem likely 
that scientific work would lead to any permanent provision, 
it became necessary for the youthful astronomer to choose 
a profession. It had been all along intended that he 
should enter the Church, though for some reason which is 
not told us, he did not take orders as soon as his age would 
have entitled him to do so. In 1719, however, the 
Bishop of Hereford offered Bradley the Yicarage of 
Bridstow, near Ross, in Monmouthshire, and on July 25th, 
1720, he having then taken priest's orders, was duly 
instituted in his vicarage. In the beginning of the next 
year, Bradley had some addition to his income from the 
proceeds of a Welsh living, which, being a sinecure, he was 
able to hold with his appointment at Bridstow. It appears, 
however, that his clerical occupations were not very 
exacting in their demands upon his time, for he was still 
able to pay long and often-repeated visits to his uncle at 
"Wandsworth, who, being himself a clergyman, seems to 
have received occasional assistance in his ministerial duties 
from his astronomical nephew. 

The time, however, soon arrived when Bradley was 
able to make a choice between continuing to exercise his 
jorofession as a divine, or devoting himself to a scientific 
career. The Savilian Professorship of Astronomy in the 
University of Oxford became vacant by the death of Dr. 
John Keill. The statutes forbade that the Savilian 
Professor should also hold ^. clerical appointment, and 


Mr. Pound would certainly have been elected to tlie pro- 
fessorship had he consented to surrender his preferments 
in the Church. But Pound, was unwilling to sacrifice 
his clerical position, and though two or three other 
candidates appeared in the field, yet the talents of Bradley 
were so conspicuous that he was duly elected, his willing- 
ness to resign the clerical profession having been first 

There can be no doubt that, with such influential friends 
as Bradley possessed, he would have made great advances 
had he adhered to his profession as a divine. Bishop 
Hoadly, indeed, with other marks of favour, had already 
made the astronomer his chaplain. The engrossing 
nature of Bradley^s interest in astronomy decided him, 
however, to sacrifice all other prospects in comparison 
with the opening afforded by the Savilian Professorship. 
It was not that Bradley found himself devoid of interest 
in clerical matters, but he felt that the true scope for such 
abilities as he possessed would be better found in the dis- 
charge of the scientific duties of the Oxford chair than 
in the spiritual charge of a parish. On April the 26th, 
1722, Bradley read his inaugural lecture in that new 
position on which he was destined to confer such lustre. 

It must, of course, be remembered that in those early 
days the art of constructing the astronomical telescope 
was very imperfectly understood. The only known method 
for getting over the peculiar difiiculties presented in the 
construction of the refracting telescope, was to have it of 
the most portentous length. In fact, Bradley made 
several of his observations with an instrument of two 
hundred and twelve feet focusi In such a case, no tub© 


could be used, and the object glass was merely fixed at 
tbe top of a bigb pole. Notwithstanding the incon- 
venience and awkwardness of such an instrument, Bradley 
by its means succeeded in making many careful measure- 
ments. He observed, for example, the transit of Mer- 
cury over the sun's disc, on October 9th, 1723 ; he also 
measured the dimensions of the planet Venus, while a 
comet which Halley discovered on October the 9th, 1723, 
was assiduously observed at Wanstead up to the middle 
of the ensuing month. The first of Bradley's remark- 
able contributions to the " Philosophical Transactions " 
relates to this comet, and the extraordinary amount of 
work that he went through in connection therewith may 
be seen from an examination of his book of Calculations 
which is still extant. 

The time was now approaching when Bradley was to 
make the first of those two great discoveries by which his 
name has acquired a lustre that has placed him in the 
very foremost rank of astronomical discoverers. As has 
been often the case in the history of science, the first of 
these great successes was attained while he was pursuing a 
research intended for a wholly difierent purpose. It had 
long been recognised that as the earth describes a vast 
orbit, nearly two hundred million miles in diameter, in its 
annual journey round the sun, the apparent places of the 
stars should alter, to some extent, in correspondence with 
the changes in the earth's position. The nearer the star 
the greater the shift in its apparent place on the heavens, 
which must arise from the fact that it was seen from 
different positions in the earth's orbit. It had been pointed 
out that these apparent changes in the places of the stars^ 



due to the movement of tlie earth, would provide the 
means of measuring the distances of the stars. As, how- 
ever, these distances are enormously great in comparison 
with the orbit which the earth describes around the sun, 
the attempt to determine the distances of the stars by the 
shift in their positions had hitherto proved ineffectual. 
Bradley determined to enter on this research once again ; 
he thought that by using instruments of greater power, 
and by making measurements of increased delicacy, he 
would be able to perceive and to measure displacements 
which had proved so small as to elude the skill of the 
other astronomers who had previously made efforts in the 
same direction. In order to simplify the investigation as 
much as possible, Bradley devoted his attention to one 
particular star. Beta Draconis, which happened to pass 
near his zenith. The object of choosing a star in this 
position was to avoid the difficulties which would be in- 
troduced by refraction had the star occupied any other 
place in the heavens than that directly overhead. 

We are still able to identify the very spot on which 
the telescope stood which was used in this memorable 
research. It was erected at the house then occupied 
by Molyneux, on the western extremity of Kew Green. 
The focal length was 24 feet 3 inches, and the eye-glass 
was 3i feet above the ground floor. The instrument was 
first set up on November 26th, 1725. If there had been 
any appreciable disturbance in the place of Beta Draconis 
in consequence of the movement of the earth around the 
sun, the star must appear to have the smallest latitude 
when in conjunction with the sun, and the greatest when 
in opposition, The star passed the meridian at noou h\ 


December, and its position was particularly noticed by 
Molyneux on the third of that month. Any perceptible 
displacement by parallax — for so the apparent change in 
, position, due to the earth's motion, is called — would 
have made the star shift towards the north. Bradley, 
however, when observing it on the 17th, was surprised to 
find that the apparent place of the star, so far from 
shifting towards the north, as they had perhaps hoped it 
would, was found to lie a little more to the south than 
when it was observed before. He took extreme care to 
be sure that there was no mistake in his observation, and, 
true astronomer as he was, he scrutinized with the utmost 
minuteness all the circumstances of the adjustment of his 
instruments. Still the star went to the south, and it 
continued so advancing in the same direction until the 
following March, by which time it had moved no less 
than twenty seconds south from the place which it 
occupied when the first observation was made. After a 
brief pause, in which no apj)arent movement was percep- 
tible, the star by the middle of April appeared to be 
returning to the north. Early in June it reached the 
same distance from the zenith which it had in December. 
By September the star was as much as thirty-nine seconds 
more to the north than it had been in March, then it re- 
turned towards the south, regaining in December the same 
situation which it had occupied twelve months before. 

This movement of the star being directly opposite to 
the movements which would have been the consequence 
of parallax, seemed to show that even if the star had any 
parallax its effects upon the apparent place were entirely 
masked by a much larger motion of a totally different 



description. Various attempts were made to account for 
tlie phenomenon, but they were not successful. Bradley 
accordingly determined to investigate the whole sub- 
ject in a more thorough manner. One of his objects 
was to try whether the same movements which he had 
observed in one star were in any similar degree pos- 
sessed by other stars. For this purpose he set up a new 
instrument at Wanstead, and there he commenced a 
most diligent scrutiny of the apparent places of several 
stars which passed at different distances from the zenith. 
He found in the course of this research that other stars 
exhibited movements of a similar description to those 
which had already proved so perplexing. For a long 
time the cause of these apparent movements seemed a 
mystery. At last, however, the explanation of these 
remarkable phenomena dawned upon him, and his great 
discovery was made. 

One day when Bradley was out sailing he happened to 

remark that every time the boat was laid on a different 

tack the vane at the top of the boat's mast shifted a little, 

as if there had been a slight change in the direction of 

the wind. After he had noticed this three or four times 

he made a remark to the sailors to the effect that it was 

very strange the wind should always happen to change 

just at the moment when the boat was going about. The 

sailors, however, said there had been no change in the 

wind, but that the alteration in the vane was due to the 

fact that the boat's course had been altered. In fact, the 

position of the vane was determined both by the course of 

the boat and the direction of the wind, and if either of 

these were altered there would be a corresponding change 


in the direction of the vane. This meant, of course, that 
the observer in the boat which was moving along would 
feel the wind coming from a point different from that 
in which the wind appeared to be blowing Avhen the 
boat was at rest, or when it was sailing in some different 
direction. Bradley's sagacity saw in this observation the 
clue to the difficulty which had so long troubled him. 

It had been discovered before the time of Bradley that 
the passage of light through space is not an instantaneous 
phenomenon. Light requires time for its journey. 
Galileo surmised that the sun may have reached the 
horizon before we see it there, and it was indeed suffi- 
ciently obvious that a physical action, like the transmission 
of light, could hardly take place without requiring some 
lapse of time. The speed with which light actually 
travelled was, however, so rapid that its determination 
eluded all the means of experimenting which were avail- 
able in those days. The penetration of Eoemer had 
previously detected irregularities in the observed times of 
the eclipses of Jupiter's satellites, which were undoubtedly 
due to the interval which light required for stretching 
across the interplanetary spaces. Bradley argued that 
as light can only travel with a certain speed, it may in a 
measure be regarded like the wind, which he noticed in 
the boat. If the observer were at rest, that is to say, if 
the earth were a stationary object, the direction in which 
the light actually does come would be different from that 
in which it appears to come when the earth is in motion. 
It is true that the earth travels but eighteen miles a 
second, while the velocity with which light is borne 
along attains to as much as 180,000 miles a second. The 


velocity of light is thus ten thousand times greater than 
the speed of the earth. But even though the wind blew 
ten thousand times faster than the speed with which the 
boat was sailing there would still be some change, though 
no doubt a very small change, in the position of the vane 
when the boat was in progress from the position which 
it would have if the boat were at rest. It therefore 
occurred to this most acute of astronomers that when the 
telescope was pointed towards a star so as to place it appa- 
rently in the centre of the field of view, yet that was not 
generally the true position of the star. It was not, in fact, 
the position in which the star would have been observed 
had the earth been at rest. Provided with this sugges- 
tion, he explained the apparent movements of the stars 
by the principle known as the *' aberration of light." 
Every circumstance was accounted for as a consequence 
of the relative movements of the earth and of the light 
from the star. This beautiful discovery not only estab- 
lished in the most forcible manner the nature of the 
movement of light ; not only did it illustrate the truth 
of the Copernican theory which asserted that the earth 
revolved around the sun, but it was also of the utmost 
importance in the improvement of practical astronomy. 
Every observer now knows that, generally speaking, 
the position which the star appears to have is not 
exactly the position in which the star does actually lie. 
The observer is, however, able, by the application of the 
principles which Bradley so clearly laid down, to apply to 
an observation the correction which is necessary to obtain 
from it the true place in which the object is actually 
situated. This memorable achievement at once conferred 


on Bradley the higliest astronomical fame. He tested his 
discovery in every way, but only to confirm its truth in 
the most complete manner. 

Halley, the Astronomer Eoyal, died on the 14th Janu- 
ary, 1742, and Bradley was immediately pointed out as 
his successor. He was accordingly appointed Astronomer 
Eoyal in February, 1742. On first taking up his abode at 
Greenwich he was unable to conduct his observations 
owing to the wretched condition in which he found the in- 
struments. He devoted himself, however, assiduously to 
their repair, and his first transit observation is recorded on 
the 25th July, 1742. He worked with such energy that 
on one day it appears that 255 transit observations were 
taken by himself alone, and in September, 1747, he had 
completed the series of observations which established his 
second great discovery, the nutation of the earth's axis. 
The way in which he was led to the detection of the nuta- 
tion is strikingly illustrative of the extreme care with 
which Bradley conducted his observations. He found that 
in the course of a twelvemonth, when the star had com- 
pleted the movement which was due to aberration, it did 
not return exactly to the same position which it had pre- 
viously occupied. At first he thought this must be due to 
some instrumental error, but after closer examination and 
repeated study of the effect as manifested by many 
different stars, he came to the conclusion that its origin 
must be sought in some quite different source. The fact 
is that a certain change takes place in the apparent position 
of the stars which is not due to the movement of the star 
itself, but is rather to be attributed to changes in the 
points from which the star's positions are measured. 


We may explain the matter in this way. As the earth 
is not a sphere, but has protuberant parts at the equator, 
the attraction of the moon exercises on those protuberant 
parts a pulling effect which continually changes the 
direction of the earth's axis, and consequently the position 
of the pole must be in a state of incessant fluctuation. The 
pole to which the earth's axis points on the sky is, there- 
fore, slowly changing. At present it happens to lie near 
the Pole Star, but it will not always remain there. It 
describes a circle around the pole of the Ecliptic, requiring 
about 25,000 years for a complete circuit. In the course 
of its progress the pole will gradually pass now near one 
star and now near another, so that many stars will in the 
lapse of ages discharge the various functions which the 
present Pole Star does for us. In about 12,000 years, for 
instance, the pole will have come near the bright star, 
Vega. This movement of the pole had been known for 
ages. But what Bradley discovered was that the pole, 
instead of describing an uniform movement as had been 
previously supposed, followed a sinuous course now on one 
side and now on the other of its mean place. This he 
traced to the fluctuations of the moon's orbit, which under- 
goes a continuous change in a period of nineteen years. 
Thus the efficiency with which the moon acts on the pro- 
tuberant mass of the earth varies, and thus the pole is 
caused to oscillate. 

This subtle discovery, if perhaps in some ways less im- 
pressive than Bradley's earlier achievements of the detec- 
tion of the aberration of light, is regarded by astronomers 
as testifying even in a higher degree to his astonishing 
care and skill as an observer, and justly entitles him 


to a unique place among the astronomers whose dis- 
coveries have been effected by consummate practical skill 
in the use of astronomical instruments. 

Of Bradley's private or domestic life there is but little 
to tell. In 1744, soon after he became Astronomer Royal, 
he married a daughter of Samuel Peach, of Chalford, in 
Gloucestershire. There was but one child, a daughter, 
who became the wife of her cousin. Rev. Samuel Peach, 
rector of Compton, Beauchamp, in Berkshire. 

Bradley's last two years of life were clouded by a 
melancholy depression of spirits, due to an apprehension 
that he should survive his rational faculties. It seems, 
however, that the ill he dreaded never came upon him, 
for he retained his mental powers to the close. He died 
on 13th July, 1762, aged seventy, and was buried at 


William Herschel, one of tlie greatest astronomers tliat 
lias ever lived, was born at Hanover, on tlie 15th Novem- 
ber, 1738. His father, Isaac Herschel, was a man evi- 
dently of considerable ability, whose life was devoted to 
the study and practice of music, by which he earned a 
somewhat precarious maintenance. He had but few 
worldly goods to leave to his children, but he more than 
compensated for this by bequeathing to them a splendid 
inheritance of genius. Touches of genius were, indeed, 
liberally scattered among the members of Isaac's large 
family, and in the case of his fourth child, William, and 
of a sister several years younger, it was united with that 
determined perseverance and rigid adherence to principle 
which enabled genius to fulfil its perfect work. 

A faithful chronicler has given us an interesting account 
of the way in which Isaac Herschel educated his sons ; 
the narrative is taken from the recollections of one who, 
at the time we are speaking of, was an unnoticed little 
girl five or six years old. She writes : — 

" My brothers were often introduced as solo performers 
and assistants in the orchestra at the Court, and I remem- 
ber that I was frequently prevented from going to sleep 


by tlie lively criticisms on music on coming from a con- 
cert. Often I would keep myself awake that I might 
listen to their animating remarks, for it made me so happy 
to see them so happy. But generally their conversation 
would branch out on philosophical subjects, when my 
brother William and my father often argued with such 
warmth that my mother's interference became necessary, 
when the names — Euler, Leibnitz, and Newton — sounded 
rather too loud for the repose of her little ones, who had 
to be at school by seven in the morning.^' The child 
whose reminiscences are here given became afterwards the 
famous Caroline Herschel. The narrative of her life, by 
Mrs. John Herschel, is a most interesting book, not only 
for the account it contains of the remarkable woman her- 
self, but also because it provides the best picture we have 
of the great astronomer to whom Caroline devoted her 

This modest family circle was, in a measure, dispersed 
at the outbreak of the Seven Years' War in 1756. The 
French proceeded to invade Hanover, which, it will be 
remembered, belonged at this time to the British domi- 
nions. Young William Herschel had already obtained 
the position of a regular performer in the regimental band 
of the Hanoverian Guards, and it was his fortune to 
obtain some experience of actual warfare in the disastrous 
battle of Hastenbeck. He was not wounded, but he had 
to spend the night after the battle in a ditch, and his 
meditations on the occasion convinced him that soldiering 
was not the profession exactly adapted to his tastes. We 
need not attempt to conceal the fact that he left his regi- 
ment by the very simple but somewhat risky process of 


desertion. He had, it would seem, to adopt disguises to 
effect his escape. At all events, by some means lie suc- 
ceeded in eluding detection and reached England in 
safety. It is interesting to have learned on good authority 
that many years after this offence was committed it was 
solemnly forgiven. When Herschel had become the 
famous astronomer, and as such visited King George at 
Windsor, the King at their first meeting handed to him 
his pardon for deserting from the army, written out in due 
form by his Majesty himself. 

It seems that the young musician must have had some 
difficulty in providing for his maintenance during the 
first few years of his abode in England. It was not until 
he had reached the age of twenty-two that he succeeded 
in obtaining any regular appointment. He was then 
made Instructor of Music to the Durham Militia. Shortly 
afterwards, his talents being more widely recognised, he 
was appointed as organist at the parish church at Halifax, 
and his prospects in life now being fairly favourable, and 
the Seven. Years' War being over, he ventured to pay a 
visit to Hanover to see his father. We can imagine the 
delight with which old Isaac Herschel welcomed his pro- 
mising son, as well as his parental pride when a concert 
was given at which some of William's compositions were 
performed. If the father was so intensely gratified on this 
occasion, what would his feelings have been could he have 
lived to witness his son's future career ? But this plea- 
sure was not to be his, for he died many years before 
William became an astronomer. 

In 1766, about a couple of years after his return to 
England from this visit to his old home, we find that 


Herschel had received a further promotion to be organist 
in the Octagon Chapel, at Bath. Bath was then, as now, 
a highly fashionable resort, and many notable personages 
patronised the rising musician. Herschel had other points 
in his favour besides his professional skill ; his appear- 
ance was good, his address was prepossessing, and even 
his nationality was a distinct advantage, inasmuch as he 
was a Hanoverian in the reign of King George the Third. 
On Sundays he played the organ, to the great delight of 
the congregation, and on week-days he was occupied by 
giving lessons to private pupils, and in preparation for 
public performances. He thus came to be busily employed, 
and seems to have been in the enjoyment of comfortable 

From his earliest youth Herschel had been endowed 
with that invaluable characteristic, an eager curiosity for 
knowledge. He was naturally desirous of perfecting him- 
self in the theory of music, and thus he was led to study 
mathematics. When he had once tasted the charms of 
mathematics, he saw vast regions of knowledge unfolded 
before him, and in this way he was induced to direct 
his attention to astronomy. More and more this pursuit 
seems to have engrossed his attention, until at last it had 
become an absorbing passion. Herschel was, however, 
still obliged, by the exigency of procuring a livelihood, 
to give up the best part of his time to his profession as a 
musician ; but his heart was eagerly fixed on another 
science, and every spare moment was steadily devoted to 
astronomy. For many years, however, he continued to 
labour at his original calling, nor was it until he had 
attained middle age and become the most celebrated 



7, New King- Street, Bath, where Herscliel lived. 

astronomer of tlie time, tliat he was enabled to concen- 
trate his attention exclusively on his favourite pursuit. 

It was with quite a small telescope which had been lent 
him by a friend that Herschel commenced his career as 
an observer. However, he speedily discovered that to 
see all he wanted to see, a telescope of far greater power 


would be necessary, and lie determined to obtain this more 
powerful instrument by actually making it with bis own 
bands. At first it may seem scarcely likely tbat one wbose 
occupation bad previously been tbe study and practice 
of music sbould meet witb success in so tecbnical an 
operation as tbe construction of a telescope. It may, 
bowever, be mentioned tbat tbe kind of instrument wbicb 
Herscbel designed to construct was formed on a very 
different principle from tbe refracting telescopes witb 
wbicb we are ordinarily familiar. His telescope was to 
be wbat is termed a reflector. In tbis type of instrument 
tbe optical power is obtained by tbe use of a mirror at 
tbe bottom of tbe tube, and tbe astronomer looks down 
tbrougb tbe tube toKarch Jiis mirror, and views tbe reflec- 
tion of tbe stars witb its aid. Its efiiciency as a telescope 
depends entirely on tbe accuracy witb wbicb tbe requisite 
form bas been imparted to tbe mirror. Tbe surface bas 
to be bellowed out a little, and tbis bas to be done so 
truly tbat tbe sligbtest deviation from good workmansbip 
in tbis essential particular would be fatal to efficient per- 
formance of tbe telescope. 

Tbe mirror tbat Herscbel emploj^ed was composed of a 
mixture of two parts of copper to one of tin ; tbe alloy 
tbus obtained is an intensely bard material, very difficult 
to cast into tbe proper sbape, and very difficult to work 
afterwards. It possesses, bowever, wben polisbed, a lustre 
bardly inferior to tbat of silver itself. Herscbel bas re- 
corded bardly any particulars as to tbe actual process by 
wbicb be cast and figured bis reflectors. "We are, bow- 
ever, told tbat in later years, after bis telescopes bad 
become famous, be made a considerable sum of money by 



William Herschel. 

the manufacture and sale of great instruments. Perhaps 
this may be the reason why he nevisr found it expedient 
to publish any very explicit details as to the means by 
which his remarkable successes were obtained. 

Since Herschel's time many other astronomers, notably 
the late Earl of Rosse, have experimented in the same 
direction, and succeeded in making telescopes certainly 
far greater, and probably more perfect, than any which 



Caroline Herschel. 

HerscLel appears to have constructed. The details of 
these later methods are now well known, and have been 
extensively practised. Many amateurs have thus been 
able to make telescopes by following the instructions so 
clearly laid down by Lord Rosse and the other authori- 
ties. Indeed, it would seem that any one who has a little 
mechanical skill and a good deal of patience ought now 
to experience no great difficulty in constructing a tele- 


scope quite as powerful as tliat whicli first brought 
Herschel into fame. I should, however, mention that in 
these modern days the material generally used for the 
mirror is of a more tractable description than the metallic 
substance which was employed by Herschel and by Lord 
Eosse. A reflecting telescope of the present day would 
not be fitted with a mirror composed of that alloy known 
as speculum metal, whose composition I have already 
mentioned. It has been found more advantageous to 
employ a glass mirror carefully figured and polished, just 
as a metallic mirror would have been, and then to impart 
to the polished glass surface a fine coating of silver laid 
down by a chemical process. The silver-on-glass mirrors 
are so much lighter and so much easier to construct that 
the more old-fashioned metallic mirrors may be said to 
have fallen into almost total disuse. In one respect, how- 
ever, the metallic mirror may still claim the advantage 
that, with reasonable care, its surface will last bright and 
untarnished for a much longer period than can the silver 
film on the glass. However, the operation of re-silvering 
a ""lass has now become such a simple one that the advan- 
tage this indicates is not relatively so great as might at 
first be supposed. 

Some years elapsed after Herschel's attention had been 
first directed to astronomy, before he reaped the reward 
of his exertions in the possession of a telescope which 
would adequately reveal some of the glories of the heavens. 
It was in 1774, when the astronomer was thirty-six years 
old, that he obtained his first glimpse of the stars with an 
instrument of his own construction. Night after night, 
as soon as his musical labours, we:ce ^nded, his telescopes 



. Street view, Herschel House, Slough. 

were brouglit out, sometimes into tlie small back garden 
of his house at Bath, and sometimes into the street in 
front of his hall-door. It was characteristic of him that 
he was always endeavouring to improve his apparatus. 
He was incessantly making fresh mirrors, or trying new 
lenses, or combinations of lenses to act as eye-pieces, or 
projecting alterations in the mounting by which the 
telescope was supported. Such was his enthusiasm that 
his house, we are told, was incessantly littered with the 
usual indications of the workman's presence, greatly to 
the distress of his sister, who, at this time, had come to 
take up her abode with him and look after his house- 
keeping. Indeed, she complained that in his astronomical 
ardour he sometimes omitted to take off, before going into 
his workshop, the beautiful lace ruffles which he wore while 
conducting a concert, and that consequently they became 


soiled with the pitch employed in the polishing of his 

This sister, who occupies such a distinct place in scien- 
tific history, is the same little girl to whom we have 
already referred. From her earliest days she seems to 
have cherished a passionate admiration for her brilliant 
brother William. It was the proudest delight of her 
childhood as well as of her mature years to render him 
whatever service she could ; no man of science was ever 
provided with a more capable or energetic helper than 
William Herschel found in this remarkable woman. What- 
ever work had to be done she was willing to bear her 
share in it, or even to toil at it unassisted if she could 
be allowed to do so. She not only managed all his 
domestic affairs, but in the grinding of the lenses and in 
the polishing of the mirrors she rendered every assistance 
that was possible. At one stage of the very delicate 
operation of fashioning a reflector, it is necessary for the 
workman to remain with his hand on the mirror for many 
hours in succession. When such labours were in progress, 
Caroline used to sit by her brother, and enliven the time 
by reading stories aloud, sometimes pausing to feed him 
with a spoon while his hands were engaged on the task 
from which he could not desist for a moment. 

When mathematical work had to be done Caroline was 
ready for it ; she had taught herself sufficient to enable 
her to perform the kind of calculations, not, perhaps, very 
difficult ones, that Herschel's work required ; indeed, it 
is not too much to say that the mighty life-work which 
this man was enabled to perform could never have been 
accomplished had it not been for the self-sacrifice of this 


ever-loving and faithful sister. When Herschel was at 
the telescope at night, Caroline sat by him at her desk, 
pen in hand, ready to write down the notes of the obser- 
vations as they fell from her brother's lips. This was no 
insignificant toil. The telescope was, of course, in the open 
air, and as Herschel not unf requently continued his obser- 
vations throughout the whole of a long winter's night, 
there were but few women who could have accomplished 
the task which Caroline so cheerfully executed. From 
dusk till dawn, when the sky was clear, were Herschel's 
observing hours, and what this sometimes implied we can 
realise from the fact that Caroline assures us she had 
sometimes to desist because the ink had actually frozen 
in her pen. The night's work over, a brief rest was 
taken, and while William had his labours for the day to 
attend to, Caroline carefully transcribed the observations 
made during the night before, reduced all the figures, and 
prepared everything in readiness for the observations that 
were to follow on the ensuing evening. 

But we have here been anticipating a little of the 
future which lay before the great astronomer ; we must 
now revert to the history of his early work, at Bath, in 
1774, when Herschel's scrutiny of the skies first com- 
menced with an instrument of his own manufacture. For 
some few years he did not attain any result of importance ; 
no doubt he made a few interesting observations, but the 
value of the work during those years is to be found, not 
in any actual discoveries which were accomplished, but in 
the practice which Herschel obtained in the use of his in- 
struments. It was not until 1782 that the great achieve- 
ment took place by which he at once sprang into fame. 



Garden view, Herschel House, Slough. 

It is sometimes said that discoveries are made by acci- 
dent, and, no doubt, to a certain extent, but only, I fanc}^, 
to a very small extent, tbis statement may be true. It 
is, at all events, certain that sucb lucky accidents do not 
often fall to tbe lot of people unless those people have 
done much to deserve them. This was certainly the case 
with Herschel. He appears to have formed a project for 
making a close examination of all the stars above a certain 
magnitude. Perhaps he intended to confine this research 
to a limited region of the sky, but, at all events, he seems 
to have undertaken the work energetically and systemati- 
cally. Star after star was brought to the centre of the 
field of view of his telescope, and after being carefully 
examined was then displaced, while another star was 


brought forward to be submitted to the same process. In 
the great majority of cases such observations yield really 
nothing of importance ; no doubt even the smallest star 
in the heavens would, if we could find out all about it, 
reveal far more than all the astronomers that were 
ever on the earth have even conjectured. What we 
actually learn about the great majority of stars is only 
information of the most meagre description. We see that 
the star is a little point of light, and we see nothing 

In the great review which Herschel undertook he 
doubtless examined hundreds, or perhaps thousands of 
stars, allowing them to pass away without note or com- 
ment. But on an ever-memorable night in March, 1782, 
it happened that he was pursuing his task among the 
stars in the Constellation of Gremini. Doubtless, on 
that night, as on so many other nights, one star after 
another w^as looked at only to be dismissed, as not re- 
quiring further attention. On the evening in question, 
however, one star was noticed which, to Herschel' s acute 
vision, seemed different from the stars which in so many 
thousands are strewn over the sky. A star properly so 
called appears merely as a little point of light, which no 
increase of magnifying power will ever exhibit with a 
true disc. But there was something in the star-like object 
which Herschel saw that immediately arrested his atten- 
tion and made him apply to it a higher magnifying 
power. This at once disclosed the fact that the object 
possessed a disc, that is, a definite, measurable size, and 
that it was thus totally different from any one of the 
hundreds and thousands of stars which exist elsewhere in 


space. Indeed, we may say at once that this little object 
was not a star at all ; it was a planet. That such was 
its true nature was confirmed, after a little further ob- 
servation, by perceiving that the body was shifting its 
place on the heavens relatively to the stars. The organist 
at the Octagon Chapel at Bath had, therefore, discovered 
a new planet with his home-made telescope. 

I can imagine some one will say, " Oh, there was 
nothing so wonderful in that; are not planets always 
being discovered ? Has not M. Palisa, for instance, dis- 
covered about eighty of such objects, and are there not 
hundreds of them known nowadays?" This is, to a 
certain extent, quite true. I have not the least desire to 
detract from the credit of those industrious and sharp- 
sighted astronomers who have in modern days brought so 
many of. these little objects within our cognisance. I 
think, however, it must be admitted that such disco- 
veries have a totally different importance in the history 
of science from that which belongs to the peerless achieve- 
ment of Herschel. In the first place, it must be observed 
that the minor planets now brought to light are so minute 
that if a score of them were rolled together into one lump 
it would not be one-thousandth part of the size of the 
grand planet discovered by Herschel. This is, neverthe- 
less, not the most important point. "What marks Her- 
schers achievement as one of the great epochs in the 
history of astronomy is the fact that the detection of 
Uranus was the very first recorded occasion of the dis- 
covery of any planet whatever. 

For uncounted ages those who watched the skies had 
been aware of the existence of the five old planets — 


Jupiter, Mercurj^, Saturn, Yenus, and Mars. It never 
seems to have occurred to any of the ancient philosophers 
that there could be other similar objects as yet undetected 
over and above the well-known five. Great then was the 
astonishment of the scientific world when the Bath organist 
announced his discovery that the five planets which had 
been known from all antiquity must now admit the com- 
pany of a sixth. And this sixth planet was, indeed, 
worthy on every ground to be received into the ranks of 
the five glorious bodies of antiquity. It was, no doubt, 
not so large as Saturn, it was certainly very much less 
than Jupiter ; on the other hand, the new body was very 
much larger than Mercury, than Venus, or than Mars, 
and the earth itself seemed quite an insignificant object 
in comparison with this newly added member of the Solar 
System. In one respect, too, Herschel's new planet was 
a much more imposing object than any one of the older 
bodies ; it swept around the sun in a majestic orbit, far 
outside that of Saturn, which had previously been regarded 
as the boundary of the Solar System, and its stately pro- 
gress required a period of not less than eighty- one years. 

King George the Third, hearing of the achievements 
of the Hanoverian musician, felt much interest in his 
discovery, and accordingly Herschel was bidden to come 
to Windsor, and to bring with him the famous telescope, 
in order to exhibit the new planet to the King, and to tell 
his Majesty all about it. The result of the interview was 
to give Herschel the opportunity for which he had so long 
wished, of being able to devote himself exclusively to 
science for the rest of his life. 

The King took so great a fancy to the astronomer that 



View of the Observatory, Herscliel House, Slough. 

he first, as I have already mentioned, duly pardoned his 
desertion from the army, some twenty-five years previ- 
ously. As a further mark of his favour the King pro- 
posed to confer on Herschel the title of his Majesty's own 
astronomer, to assign to him a residence near Windsor, 
to provide him with a salary, and to furnish such funds 
as might be required for the erection of great telescopes, 
and for the conduct of that mighty scheme of celestial 
observation on which Herschel was so eager to enter. 
HerscheFs capacity for work would have been much 
impaired if he had been deprived of the aid of his admir- 
able sister, and to her, therefore, the King also assigned 
a salary, and she was installed as Herschers assistant in 
his new post. 

With his usually impulsive determination, Herschel 
immediately cut himself free from all his musical avoca- 



tions at Bath, and at once entered on the task of making 
and erecting the great telescopes at Windsor. There, for 
more than thirty years, he and his faithful sister prose- 
cuted with unremitting ardour their nightly scrutiny of 
the sky. Paper after paper was sent to the Royal Society, 
describing the hundreds, indeed the thousands, of objects 
such as double stars ; nebulee and clusters, which were first 
revealed to human gaze during those midnight vigils. 
To the end of his life he still continued at every possible 
opportunity to devote himself to that beloved pursuit in 
which he had such unparalleled success. No single dis« 
covery of Herschers later years was, however, of the 
same momentous description as that which first brought 
him to fame. 

The 40 -foot telescope as it was in the year 1863, Herschel House, Slough. 


Herschel married when considerably advanced in life, 
and lie lived to enjoy the indescribable pleasure of finding 
that his only son, afterwards Sir John Herschel, was 
treading worthily in his footsteps, and attaining renown 
as an astronomical observer, second only to that of his 
father. The elder Herschel died in 1822, and his illus- 
trious sister Caroline then returned to Hanover, where 
she lived for many years to receive the respect and atten- 
tion which were so justly hers. She died at a very 
advanced age in 1848. 


The author of the *' Mecanlque Celeste " was born at 
J3eaumont-en-Auge, near Honfleur, in 1749, just thirteen 
years later than his renowned friend Lagrange. His 
father was a farmer, but appears to have been in a position 
to provide a good education for a son who seemed promis- 
ing. Considering the unorthodoxy in religious matters 
which is generally said to have characterized Laplace in 
later years, it is interesting to note that when he was a 
boy the subject which first claimed his attention was 
theology. He was, however, soon introduced to the study 
of mathematics, in which he presently became so pro- 
ficient, that while he was still no more than eighteen years 
old, he obtained employment as a mathematical teacher in 
his native town. 

Desiring wider opportunities for study and for the 
acquisition of fame than could be obtained in the narrow 
associations of provincial life, young Laplace started for 
Paris, being provided with letters of introduction to 
D'Alemberfc, who then occupied the most prominent posi- 
tion as a mathematician in France, if not in the whole of 
Europe. D'Alembert's fame was indeed so brilliant that 
Catherine the Great wrote to ask him to undertake the 


education of lier son, and promised the splendid income of a 
hundred thousand francs. He preferred, however, a quiet 
life of research in Paris, although there was but a modest 
salary attached to his oflSce. The philosopher accordingly 
declined the alluring offer to go to E-ussia, even though 
Catherine wrote again to say : *' I know that your refusal 
arises from your desire to cultivate your studies and your 
friendships in quiet. But this is of no consequence : bring 
all your friends with you, and I promise you that both 
you and they shall have every accommodation in my 
power." With equal firmness the illustrious mathe- 
matician resisted the manifold attractions with which 
Frederick the Great sought to induce him to take up his 
residence at Berlin. In reading of these invitations we 
cannot but be struck at the extraordinary resj)ect which 
was then paid to scientific distinction. It must be re- 
membered that the discoveries of such a man as D'Alem- 
bert were utterly incapable of being appreciated except 
by those who possessed a high degree of mathematical 
culture. We nevertheless find the potentates of Rus- 
sia and Prussia entreating and, as it happens, vainly 
entreating, the most distinguished mathematician in 
France to accept the positions that they were proud to 
offer him. 

It was to D'Alembert, the profound mathematician, that 
young Laplace, the son of the country farmer, presented 
his letters of introduction. But those letters seem to have 
elicited no reply, whereupon Laplace wrote to D'Alembert 
submitting a discussion of some point in Dynamics. This 
letter instantly produced the desired effect. D'Alembert 
thought that such mathematical talent as the young man 


displayed was in itself the best of introductions to his 
favour. It could not be overlooked, and accordingly he in- 
vited Laplace to come and see him. Laplace, of course, 
presented himself, and ere long D'Alembert obtained for 
the rising philosopher a professorship of mathematics in 
the Military School in Paris. This gave the brilliant 
young mathematician the opening for which he sought, 
and he quickly availed himself of it. 

Laplace was twenty-three years old when his first 
memoir on a profound mathematical subject appeared in 
the Memoirs of the Academy at Turin. From this time 
onwards we find him publishing one memoir after another 
in which he attacks, and in many cases successfully 
vanquishes, profound difficulties in the application of the 
IN^ewtonian theory of gravitation to the explanation of the 
solar system. Like his great contemporary Lagrange, 
he loftily attempted problems which demanded con- 
summate analytical skill for their solution. The attention 
of the scientific world thus became riveted on the 
splendid discoveries which emanated from these two men, 
each gifted with extraordinary genius. 

Laplace's most famous work is, of course, the '^ Meca- 
nique Celeste,'' in which he essayed a comprehensive 
attempt to carry out the principles which JSTewton had 
laid down, into much greater detail than JSTewton had 
found practicable. The fact was that JN^ewton had not only 
to construct the theory of gravitation, but he had to invent 
the mathematical tools, so to speak, by which his theory 
could be applied to the explanation of the movements of 
the heavenly bodies. In the course of the century which 
had elapsed between the time of Newton and the time of 


Laplace, mathematics had been extensively developed. 
In particular, that potent instrument called the infinitesimal 
calculus, which Newton had invented for the investigation 
of nature, had become so far perfected that Laplace, when 
he attempted to unravel the movements of the heavenly 
bodies, found himself provided with a calculus far more 
efficient than that which had been available to Newton. 
The purely geometrical methods which Newton employed, 
though they are admirably adapted for demonstrating in 
a general way the tendencies of forces and for explaining 
the more obvious phenomena by which the movements of 
the heavenly bodies are disturbed, are yet quite inadequate 
for dealing with the more subtle effects of the Law of 
Gravitation. The disturbances which one planet exercises 
upon the rest can only be fully ascertained by the aid of 
long calculation, and for these calculations analytical 
methods are required. 

With an armament of mathematical methods which had 
been perfected since the days of Newton by the labours of 
two or three generations of consummate mathematical 
inventors, Laplace essayed in the '' Mecanique Celeste '^ 
to unravel the mysteries of the heavens. It will hardly 
be disputed that the book which he has produced is one of 
the most difficult books to understand that has ever been 
written. In great part, of course, this difficulty arises 
from the very nature of the subject, and is so far un- 
avoidable. No one need attempt to read the ''Mecanique 
Celeste " who has not been naturally endowed with con- 
siderable mathematical aptitude which he has cultivated 
by years of assiduous study. The critic will also note 
that there are grave defects in Laplace's method of treat- 


mcnt. The style is often extremely obscure, and the 
author frequently leaves great gaps in his argument, to 
the sad discomfiture of his reader. Nor does it mend 
matters to say, as Laplace often does say, that it is '' easy 
to see '* how one step follows from another. Such infer- 
ences often present great diihculties even to excellent 
mathematicians. Tradition indeed tells us that when 
Laplace had occasion to refer to his own book, it sometimes 
happened that an argument which he had dismissed 
with his usual formula, " II est facile a voir," cost the 
illustrious author himself an hour or two of hard thinking 
before he could recover the train of reasoning which had 
been omitted. But there are certain parts of this great 
work which have always received the enthusiastic admira- 
tion of mathematicians. Laplace has, in fact, created 
whole tracts of science, some of which have been sub- 
sequently developed with much advantage in the prosecu- 
tion of the study of Nature. 

Judged by a modern code the gravest defect of La- 
place's great work is rather of a moral than of a mathe- 
matical nature. Lagrange and he advanced together in 
their study of the mechanics of the heavens, at one time 
perhaps along parallel lines, while at other times they 
pursued the same problem by almost identical methods. 
Sometimes the important result was first reached by La- 
grange, sometimes it was Laplace who had the good for- 
tune to make the discovery. It would doubtless be a diffi- 
cult matter to draw the line which should exactly sej)arate 
the contributions to astronomy made by one of these 
illustrious mathematicians, and the contributions made by 
the other. But in his great work Laplace in the loftiest 


manner disdained to accord more than the very barest 
recognition to Lagrange, or to any of the other mathe- 
maticians, Newton alone excepted, who had advanced our 
knowledge of the mechanism of the heavens. It would 
be quite impossible for a student who confined his read- 
ing to the " Mecanique Celeste ^' to gather from any indica- 
tions that it contains whether the discoveries about which 
he was reading had been really made by Laplace himself 
or whether they had not been made by Lagrange, or by 
Euler, or by Clairaut. With our present standard of 
morality in such matters, any scientific man who now 
brought forth a work in which he presumed to ignore in 
this wholesale fashion the contributions of others to the 
subject on which he was writing, would be justly censured 
and bitter controversies would undoubtedly arise. Perhaps 
we ought not to judge Laplace by the standard of our own 
time, and in any case I do not doubt that Laplace might 
have made a plausible defence. It is well known that 
when two investigators are working at the same subjects, 
and constantly publishing their results, it sometimes be- 
comes difficult for each investigator himself to distinguish 
exactly between what he has accomplished and that which 
must be credited to his rival. Laplace may probably have 
said to himself that he was going to devote his energies 
to a great work on the interpretation of Nattire, that it 
would take all his time and all his faculties, and all the 
resources of knowledge that he could command, to deal 
justly with the mighty problems before him. He would 
not allow himself to be distracted by any side issue. He 
could not tolerate that pages should be wasted in merely 
discussing to whom we owe each formula, and to whom 



each deduction from such, formula is due. He would 
rather endeavour to produce as complete a picture as he 
possibly could of the celestial mechanics, and whether it 
were by means of his mathematics alone, or whether the 
discoveries of others may have contributed in any degree 
to the result, is a matter so infinitesimally insignificant 
in comparison with the grandeur of his subject that he 
would altogether neglect it. " If Lagrange should think," 
Laplace might say, *' that his discoveries had been unduly 
appropriated, the proper course would be for him to do 
exactly what I have done. Let him also write a " Me- 
canique Celeste," let him employ those consummate talents 
which he possesses in developing his noble subject to the 
utmost. Let him utilise every result that I or any other 
mathematician have arrived at, but not trouble himself 
unduly with unimportant historical details as to who dis- 
covered this, and who discovered that ; let him produce 
such a work as he could write, and I shall heartily welcome 
it as a splendid contribution to our science." Certain it is 
that Laplace and Lagrange continued the best of friends, 
and on the death of the latter it was Laplace who was 
summoned to deliver the funeral oration at the grave of 
his great rival. 

The investigations of Laplace are, generally speaking, 
of too technical a character to make it possible to set forth 
any account of them in such a work as the present. He 
did publish, however, one treatise, called the "Systeme 
du Monde," in which, without introducing mathematical 
symbols, he was able to give a general account of the 
theories of the celestial movements, and of the discoveries 
to which he and others had been led. In this work tbe 



great French astronomer sketched for the first time that 
remarkable doctrine by which his name is probably most 
generally known to those readers of astronomical books 
who are not specially mathematicians. It is in the 
*' Systeme du Monde " that Laplace laid down the prin- 
ciples of the Nebular Theory which, in modern days, has 
been generally accepted by those philosophers who are 
competent to judge, as substantially a correct expression 
of a great historical fact. 

The Nebular Theory gives a physical account of the 
origin of the solar system, consisting of the sun in the 
centre, with the planets and their attendant satellites. 
Laplace perceived the significance of the fact that all the 
planets revolved in the same direction around the sun ; 
he noticed also that the movements of rotation of the 
planets on their axes were performed in the same direc- 
tion as that in which a planet revolves around the sun ; he 
saw that the orbits of the satellites, so far at least as he 
knew them, revolved around their primaries also in the 
same direction. Nor did it escape his attention that the 
sun itself rotated on its axis in the same sense. His philo- 
sophical mind was led to reflect that such a remarkable 
unanimity in the direction of the movements in the solar 
system demanded some special explanation. It would have 
been in the highest degree improbable that there should have 
been this unanimity unless there had been some physical 
reason to account for it. To appreciate the argument 
let us first concentrate our attention on three particular 
bodies, namely the earth, the sun, and the moon. First 
the earth revolves around the sun in a certain direc- 
tioiij and the earth also rQtatea on its axis. The direct 




tion in wliicli tlie earth turns in accordance witii tliis 
latter movement might have been that in which it revolves 
around the sun, or it might of course have been opposite 
thereto. As a matter of fact the two agree. The moon 
in its monthly revolution around the earth follows also 
the same direction, and our satellite rotates on its axis 
in the same period as its monthly revolution, but in doing 
BO is again observing this same law, We have therefore 


in the earth and moon four movements, all taking place 
in the same direction, and this is also identical with that 
in which the sun rotates once every twenty-five days. 
Such a coincidence would be very unlikely unless there 
were some physical reason for it. Just as unlikely would 
it be that in tossing a coin five heads or five tails should 
follow each other consecutively. If we toss a coin five 
times the chances that it will turn up all heads or all 
tails is but a small one. The probability of such an 
event is only one-sixteenth. 

There are, however, in the solar system many other 
bodies besides the three just mentioned which are ani- 
mated by this common movement. Among them are, 
of course, the great planets, Jupiter, Saturn, Mars, 
Venus, and Mercury, and the satellites which attend on 
these planets. All these planets rotate on their axes in 
the same direction as they revolve around the sun, and 
all their satellites revolve also in the same way. Confining 
our attention merely to the earth, the sun, and the five 
great planets with which Laplace was acquainted, we 
have no fewer than six motions of revolution and seven 
motions of rotation, for in the latter we include the 
rotation of the sun. "We have also sixteen satellites 
of the planets mentioned whose revolutions round their 
primaries are in the same direction. The rotation of the 
moon on its axis may also be reckoned, but as to the 
rotations of the satellites of the other planets we cannot 
speak with any confidence, as they are too far off to be 
observed with the necessary accuracy. "We have thus 
thirty circular movements in the solar system connected 
with the sun and moon and those great planets than which 


no others were known in the days of Laplace. The sig- 
nificant fact is that all these thirty movements take place 
in the same direction. That this should be the case with- 
out some physical reason would be just as unlikely as that 
in tossing a coin thirty times it should turn up all heads 
or all tails every time without exception. 

"We can express the argument numerically. Calculation 
proves that such an event would not generally happen 
oftener than once out of five hundred millions of trials. 
To a philosopher of Laplace's penetration, who had made 
a special study of the theory of probabilities, it seemed 
well-nigh inconceivable that there should have been such 
unanimity in the celestial movements, unless there had 
been some adequate reason to account for it. We might, 
indeed, add that if we were to include all the objects 
which are now known to belong to the solar system, the 
argument from probability might be enormously increased 
in strength. To Laplace the argument appeared so con- 
clusive that he sought for some physical cause of the 
remarkable phenomenon which the solar system presented. 
Thus it was that the famous Nebular Hypothesis took its 
rise. Laplace devised a scheme for the origin of the sun 
and the planetary system, in which it would be a necessary 
consequence that all the movements should take place in 
the same direction as they are actually observed to do. 

Let us suppose that in the beginning there was a 
gigantic mass of nebulous material, so highly heated that 
the iron and other substances which now enter into the 
composition of the earth and planets were then suspended 
in a state of vapour. There is nothing unreasonable in 
such a supposition ; indeed, we know as a matter of fact 


that there are thoasands of such nebulae to be discerned 
at present through our telescopes. It would be extremely 
unlikely that any object could exist without possessing 
some motion of rotation ; we may in fact assert that for 
rotation to be entirely absent from the great primaeval 
nebula would be almost infinitely improbable. As ages 
rolled on, the nebula gradually dispersed away by 
radiation its original stores of heat, and, in accordance 
with well-known physical principles, the materials of 
which it was formed would tend to coalesce. The greater 
part of those materials would become concentrated in a 
mighty mass surrounded by outlying uncondensed vapours. 
There would, however, also be regions throughout the 
extent of the nebula, in which subsidiary centres of 
condensation would be found. In its long course of 
cooling, the nebula would, therefore, tend ultimately to 
form a mighty central body with a number of smaller 
bodies disposed around it. As the nebula was initially 
endowed with a movement of rotation, the central mass 
into which it had chiefly condensed would also revolve, 
and the subsidiary bodies would be anim^ated by move- 
ments of revolution around the central body. These 
movements would be all pursued in one common direction, 
and it follows, from well-known mechanical principles, 
that each of the subsidiary masses, besides participating 
in the general revolution around the central body, would 
also possess a rotation around its axis, which must likewise 
be performed in the same direction. Around the sub- 
sidiary bodies other objects still smaller would be formed, 
just as they themselves were formed relatively to the 
great central mass. 


As the ages sped by, and the heat of these bodies 
became gradually dissipated, the various objects would 
coalesce, first into molten liquid masses, and thence, at a 
further stage of cooling, they would assume the appear- 
ance of solid masses, thus producing the planetary bodies 
such as we now know them. The great central mass, on 
account of its preponderating dimensions, would still re- 
tain, for further uncounted ages, a large quantity of its 
primeval heat, and would thus display the splendours of 
a glowing sun. In this way Laplace was able to account 
for the remarkable phenomena presented in the move- 
ments of the bodies of the solar system. There are many 
other points also in which the nebular theory is known 
to tally with the facts of observation. In fact, each 
advance in science only seems to make it more certain 
that the Nebular Hypothesis substantially represents the 
way in which our solar system has grown to its present 

Not satisfied with a career which should be merely 
scientific, Laplace sought to connect himself with public 
affairs. Napoleon appreciated his genius, and desired to 
enlist him in the service of the State. Accordingly he 
appointed Laplace to be Minister of the Interior. The 
experiment was not successful, for he was not by nature 
a statesman. Napoleon was much disappointed at the 
ineptitude which the great mathematician showed for 
ofiicial life, and, in despair of Laplace's capacity as an 
administrator, declared that he carried the spirit of his 
infinitesimal calculus into the management of business. 
Indeed, Laplace's political conduct hardly admits of much 
defence. "While he accepted the honours which Napoleon 


showered on him in the time of his prosperity, he seems 
to have forgotten all this when Napoleon could no longer 
render him service. Laplace was made a Marquis by 
Louis XYIIL, a rank which he transmitted to his son, 
who was born in 1789. During the latter part of his life 
the philosopher lived in a retired country place at 
Arcueile. Here he pursued his studies, and by strict 
abstemiousness, preserved himself from many of the infir- 
mities of old age. He died on March the 5th, 1827, in 
his seventy- eighth year, his last words being, " What we 
know is but little, what we do not know is immense." 


Provost Baldwin held absolute sway in the University 
of Dublin for forty-one years. His memory is well pre- 
served there. The Bursar still dispenses the satisfactory 
revenues which Baldwin left to the College. None of us 
ever can forget the marble angels round the figure of the 
dying Provost on which we used to gaze during the pangs 
of the Examination Hall. 

Baldwin died in 1785, and was succeeded by Francis 
Andrews, a Fellow of seventeen years' standing. As to 
the scholastic acquirements of xlndrews, all I can find is a 
statement that he was complimented by the polite Profes- 
sors of Padua on the elegance and purity with which he 
discoursed to them in Latin. Andrews was also reputed 
to be a skilful lawyer. He was certainly a Privj^ 
Councillor and a prominent member of the Irish House of 
Commons, and his social qualities were excellent. Perhaps 
it was Baldwin's example that stimulated a desire in 
Andrews to become a benefactor to his college. He 
accordingly bequeathed a sum of £3,000 and an annual 
income of £250 wherewith to build and endow an astro- 
nomical Observatory in the University. The figures just 
stated ought to be qualified by the words of cautious 


Ussher (afterwards the first Professor of Astronomy), that 
" this money was to arise from an accumulation of a part 
of his property, to commence upon a particular contin- 
gency happening to his family." The astronomical en- 
dowment was soon in jeopardy by litigation. Andrews 
thought he had provided for his relations by leaving to 
them certain leasehold interests connected with the Pro- 
Tost's estate. The law courts, how^ever, held that these 
interests were not at the disposal of the testator, and 
handed them over to Hely Hutchinson, the next Provost. 
The disappointed relations then petitioned the Irish Par- 
liament to redress this grievance by transferring to them 
the moneys designed by Andrews for the Observatory. 
It would not be right, they contended, that the kindly 
intentions of the late Provost towards his kindred should 
be frustrated for the sake of maintaining what they 
described as *' a purely ornamental institution." The 
authorities of the College protested against this claim. 
Counsel were heard, and a Committee of the House made 
a report declaring the situation of the relations to be a 
hard one. Accordingly, a compromise w^as made, and the 
dispute terminated. 

The selection of a site for the new astronomical Obser- 
vatory was made by the Board of Trinity College. The 
beautiful neighbourhood of Dublin offered a choice of 
excellent localities. On the north side of the Liffey an 
Observatory could have been admirably placed, either on 
the remarkable promontory of Howth or on the elevation 
of which Dunsink is the summit. On the south side of 
Dublin there are several eminences that would have been 
suitable : the breezy heaths at Foxrock combine all neces- 


sary conditions; the obelisk hill at Ivilliney would have 
given one of the most picturesque sites for an Observatory 
in the world ; while near Delgany two or three other 
good situations could be mentioned. But the Board of 
those pre-railway days was naturally guided by the ques- 
tion of proximity. Dunsink was accordingly chosen as 
the most suitable site within the distance of a reasonable 
walk from Trinity College. 

The northern boundary of the Phoenix Park approaches 
the little river Tolka, which winds through a succession 
of delightful bits of sylvan scenery, such as may be found 
in the wide demesne of Abbotstown and the classic shades 
of Glasnevin. From the banks of the Tolka, on the 
opposite side of the park, the pastures ascend in a gentle 
slope to culminate at Dunsink, where at a distance of half- 
a-mile from the stream, of four miles from Dublin, and at 
a height of 300 feet above the sea, now stands the Obser- 
vatory. From the commanding position of Dunsink a 
magnificent view is obtained. To the east the sea is 
visible, while the southern prospect over the valley of the 
Liffey is bounded by a range of hills and mountains 
extending from Killiney to Bray Head, thence to the 
little Sugar Loaf, the Two Eock and the Three Eock 
Mountains, over the flank of which the summit of the 
Great Sugar Loaf is just perceptible. Directly in front 
opens the fine valley of Glenasmole, with Kippure Moun- 
tain, while the range can be followed to its western extre- 
mity at Lyons. The climate of Dunsink is well suited 
for astronomical observation. No doubt here, as elsewhere 
in Ireland, clouds are abundant, but mists or haze are 
comparatively unusual, and fogs are almost unknown. 


Tlie legal formalities to be observed in assuming occu- 
pation exacted a delay of many months ; accordingly, it 
was not until tbe lOth December, 1782, tbat a contract 
could be made with. Mr. Graham Moyers for the erection 
of a meridian-room and a dome for an equatorial, in con- 
junction with a becoming residence for the astronomer. 
Before the work was commenced at Dunsink, the Board 
thought it expedient to appoint the first Professor of 
Astronomy. They met for this purpose on the 22nd 
January, 1783, and chose the Eev. Henry Ussher, a 
Senior Fellow of Trinity College, Dublin. The wisdom 
of the appointment was immediately shown by the assi- 
duity with which Ussher engaged in founding the obser- 
vatory. In three years he had erected the buildings and 
equipped them with instruments, several of which were of 
his own invention. On the 19th of February, 1785, a 
special grant of £200 was made by the Board to Dr. 
Ussher as some recompense for his labours. It happened 
that the observatory was not the only scientific institution 
which came into being in Ireland at this period ; the 
newly-kindled ardour for the pursuit of knowledge led, 
at the same time, to the foundation of the Royal Irish 
Academy. By a fitting coincidence, the first memoir pub- 
lished in the Transactions of the Royal Irish Academy was 
by the first Andrews, Professor of Astronomy. It was 
read on the 13th of June, 1785, and bore the title, '* Ac- 
count of the Observatory belonging to Trinity College,'' 
by the Eev. H. Ussher, ,D.D., M.R.I.A., F.E.s! This 
communication shows the extensive design that had been 
originally intended for Dunsink, only a part of which 
was, however, carried out. For instance, two long corri- 


dors, running north and south from the central edifice, 
which are figured in the paper, never developed into bricks 
and mortar. "We are not told why the original scheme had 
to be contracted ; but perhaps the reason may be not uncon- 
nected with a remark of Ussher's, that the College had 
already advanced from its own funds a sum considerably 
exceeding the original bequest. The picture of the 
building shows also the dome for the South equatorial, 
which was erected many years later. 

Ussher died in 1790. During his brief career at the 
observatory, he observed eclipses, and is stated to have 
done other scientific work. The minutes of the Board 
declare that the infant institution had already obtained 
celebrity by his labours, and they urge the claims of 
his widow to a pension, on the ground that the disease 
from which he died had been contracted by his nightly 
vigils. The Board also promised a grant of fifty guineas 
as a help to bring out Dr. Ussher's sermons. They 
advanced twenty guineas to his widow towards the pub- 
lication of his astronomical papers. They ordered his 
bust to be executed for the observatory, and offered 
"The Death of Ussher" as the subject of a prize essay; 
but, so far as I can find, neither the sermons nor the 
papers, neither the bust nor the prize essay, ever came 
into being. 

There was keen competition for the chair of Astronomy 
which the death of Tlssher vacated. The two candidates 
were Eev. John Brinkley, of Caius College, Cambridge, a 
Senior Wrangler (born at Woodbridge, Suffolk, in 1763), 
and Mr. Stack, Fellow of Trinity College, Dublin, and 
author of a book on Optics. A majority of the Board at 


first supported Stack, while Provost Hely Hiitcliinson and 
one or two others supported Brinkley. In those days the 
Provost had a veto at elections, so that ultimately Stack 
was withdrawn and Brinkley was elected. This took 
place on the 11th December, 1790. The national press 
of the day commented on the preference shown to the 
young Englishman, Brinkley, over his Irish rival. An 
animated controversy ensued. The Provost himself con- 
descended to enter the lists and to vindicate his policy 
by a long letter in the Public Register or Freeman's Journal, 
of 21st December, 1790. This letter was anonymous, but 
its authorship is obvious. It gives the correspondence 
with Maskelyne and other eminent astronomers, whose 
advice and guidance had been sought by the Provost. It 
also contends that " the transactions of the Board ought 
not to be canvassed in the newspapers." Por this refer- 
ence, as well as for much other information, I am indebted 
to my friend, the Pev. John Stubbs, D.D. 

The next event in the history of the Observatory was 
the issue of Letters Patent (32 Geo. III., a.d. 1792), in 
which it is recited that " We grant and ordain that there 
shall be for ever hereafter a Professor of Astronomy, on 
the foundation of Dr. Andrews, to be called and known 
by the name of the Poyal Astronomer of Ireland." The 
Letters prescribe the various duties of the astronomer 
and the mode of his election. They lay down regulations 
as to the conduct of the astronomical work, and as to the 
choice of an assistant. They direct that the Provost and 
Senior Fellows shall make a thorough inspection of the 
observatory once every year in June or July ; and this 
duty was Urst undertaken on the 5th of July, 1792, It 



s '^ 






may be noted that the date on which the celebration of 
the tercentenary of the University was held happens to 
coincide with the centenary of the first visitation of the 
observatory. . The visitors on the first occasion were : 
A. Murray, Matthew Young, George Hall, and John 
Barrett. They record that they find the buildings, books, 
and instruments in good condition ; but the chief feature 
in this report, as well as in many which followed it, 
related to a circumstance to which we have not yet 

In the original equipment of the observatory, Ussher, 
with the natural ambition of a founder, desired to place 
in it a telescope of more magnificent proportions than 
could be found anywhere else. The Board gave a spirited 
support to this enterprise, and negotiations were entered 
into with the most eminent instrument-maker of those 
days. This was Jesse Ramsden (1735 — 1800), famous as 
the improver of the sextant, as the constructor of the 
great theodolite used by General E,oy in the English 
Survey, and as the inventor of the dividing engine for 
graduating astronomical instruments. E-amsden had built 
for Sir George Schuckburgh the largest and most perfect 
equatorial ever attempted. He had constructed mural 
quadrants for Padua and Yerona, which elicited the won- 
der of astronomers when Dr. Maskelyne declared he could 
detect no error in their graduation so large as two seconds 
and a half. But Kamsden maintained that even better 
results would be obtained by superseding the entire quad- 
rant by the circle. He obtained the means of testing this 
prediction when he completed a superb circle for Palermo 
of five feet diameter. Finding his anticipations were 


realised, he desired to apply the same jji'inciples on a still 
grander scale. E-amsden was in this mood when he met 
with Dr. Ussher. The enthusiasm of the astronomer and 
the instrument-maker communicated itself to the Board, 
and a tremendous circle, to be ten feet in diameter, was 
forthwith projected. 

Projected, but never carried out. After Ramsden had 
to some extent completed a 10 -foot circle, he found such 
difficulties that he tried a 9 -foot, and this again he dis- 
carded for an 8-foot, which was ultimately accomplished, 
though not entirely by himself. Notwithstanding the 
contraction from the vast proportions originally designed, 
the completed instrument must still be regarded as a 
colossal piece of astronomical workmanship. Even at 
this day I do not know that any other observatory can 
show a circle eight feet in diameter graduated all round. 

I think it is Professor Piazzi Smith who tells us how 
grateful he was to find a large telescope he had ordered 
finished by the opticians on the very day they had pro- 
mised it. The day was perfectly correct ; it was only the 
year that was wrong. A somewhat remarkable experi- 
ence in this direction is chronicled by the early reports of 
the visitors to Dunsink Observatory. I cannot find the 
date on which the great circle was ordered from Rams- 
den, but it is fixed with sufficient precision by an allusion 
in Ussher's paper to the Eoyal Irish Academy, which 
shows that by the 13th June, 1785, the order had been 
given, but that the abandonment of the 10-foot scale had 
not then been contemplated. It was reasonable that the 
board should allow Hamsden ample time for the comple- 
tion of a work at once so elaborate and so novel. It could 



not have been finislied in a year, nor would there have 
been much reason for complaint if the maker had found 
he required two or even three years more. 

Seven years gone, and still no telescope, was the condi- 
tion in which the Board found matters at their first visi- 
tation in 1792. They had, however, assurances from 
E-amsden that the instrument would be completed within 
the year ; but, alas for such promises, another seven years 
rolled on, and in 1799 the place for the great circle was 
still vacant at Dunsink. E,amsden had fallen into bad 
health, and the Board considerately directed that ** in- 
quiries should be made.^^ Next year there was still no 
progress, so the Board were roused to threaten Ramsden 
with a suit at law ; but the menace was never executed, 
for the malady of the great optician grew worse, and he 
died that year. 

Affairs had now assumed a critical aspect, for the Col- 
lege had advanced much money to Ramsden during these 
fifteen years, and the instrument was still unfinished. 
An appeal was made by the Provost to Dr. Maskelyne, 
the Astronomer Royal of England, for his advice and 
kindly oflBces in this emergency. Maskelyne responds — 
in terms calculated to allay the anxiety of the Bursar — 
" Mr. Ramsden has left property behind him, and the 
College can be in no danger of losing both their money 
and the instrument." The business of Ramsden was then 
undertaken by Berge, who proceeded to finish the great 
circle quite as deliberately as his predecessor. After 
four years Berge promised the instrument in the follow- 
ing August, but it did not come. Two years later (1806) 
the Professor complains that he can get no answer from 


Berge. In 1807, it is stated that Berge will send the 
telescope in a month. He did not ; but in the next year 
(1808), about twenty-three years after the great circle 
was ordered, it was erected at Dunsink, where it is still 
to be seen. 

The following circumstances have been authenticated by 
the signatures of Provosts, Proctors, Bursars, and other 
College dignitaries : — In 1793 the Board ordered two of 
the clocks at the observatory to be sent to Mr. Cros- 
thwaite for repairs. Seven years later, in 1800, Mr. 
Crosthwaite was asked if the clocks were ready. This 
impatience was clearly unreasonable, for even in four 
more years, 1804, we find the two clocks were still in 
hand. Two years later, in 1806, the Board determined 
to take vigorous action by asking the Bursar to call upon 
Crosthwaite. This evidently produced some effect, for 
in the following year, 1807, the Professor had no doubt 
that the clocks would be speedily returned. After eight 
years more, in 1815, one of the clocks was still being 
repaired, and so it was in 1816, which is the last record 
we have of these interesting timepieces. Astronomers 
are, however, accustomed to deal with such stupendous 
periods in their calculations, that even the time taken to 
repair a clock seems but small in comparison. 

The long tenure of the chair of Astronomy by Brinkley 
is divided into two nearly equal periods by the year in 
which the great circle was erected. Brinkley was eighteen 
years waiting for his telescope, and he had eighteen years 
more in which to use it. During the first of these periods 
Brinkley devoted himself to mathematical research ; 
during the latter he became a celebrated astronomer. 


Brinkley's mathematical labours procured for their author 
some reputation as a mathematician. They appear to be 
works of considerable mBthematical elegance, but not 
indicating any great power of original thought. Per- 
haps it has been prejudicial to Brinkley's fame ia this 
direction, that he was immediately followed in his chair 
by so mighty a genius as William Rowan Hamilton. 

After the great circle had been at last erected, 
Brinkley was able to begin his astronomical work in 
earnest. Nor was there much time to lose. He was 
already forty- five years old, a year older than was 
Herschel when he commenced his immortal career at 
Slough. Stimulated by the consciousness of having the 
command of an instrument of unique perfection, Brinkley 
loftily attempted the very highest class of astronomical 
research. He resolved to measure anew with his own 
eye and with his own hand the constants of aberration 
and of nutation. He also strove to solve that great 
problem of the universe, the discovery of the distance of 
a fixed star. 

These were noble problems, and they were nobly 
attacked. But to appraise with justice this work of 
Brinkley, done seventy years ago, we must not apply to 
it the same criterion as we would think right to apply to 
similar work were it done now. We do not any longer 
use Brinkley's constant of aberration, nor do we now 
think that Brinkley's determinations of the star distances 
were reliable. But, nevertheless, his investigations exer- 
cised a marked influence on the progress of science ; they 
stimulated the study of the principles on which exact 
measurements were to be conducted. 


Brinklej^ had another profession in addition to that of 
an astronomer. He was a divine. When a man endea- 
vours to pursue two distinct occupations concurrently, it 
will be equally easy to explain why his career should be 
successful, or why it should be the reverse. If he suc- 
ceeds, he will, of course, exemplify the wisdom of having 
two strings to his bow. Should he fail, it is, of course, 
because he has attempted to sit on two stools at once. In 
Brinkley's case, his two professions must be likened to 
the two strings rather than to the two stools. It is true 
that his practical experience of his clerical life was very 
slender. He had made no attempt to combine the routine 
of a parish with his labours in the observatory. !N^or do 
we associate a special eminence in any department of 
religious work with his name. If, however, we are to 
measure Brinkley's merits as a divine by the ecclesiastical 
preferment which he received, his services to theology 
must have rivalled his services to astronomy. Having 
been raised step by step in the Church, he was at last 
appointed to the See of Cloyne, in 1826, as the successor 
of Bishop Berkelej^ 

Now, though it was permissible for the Archdeacon to 
be also the Andrews Professor, yet when the Archdeacon 
became a Bishop, it was understood that he should trans- 
fer his residence from the observatory to the palace. 
The chair of Astronomy accordingly became vacant. 
Brinkley's subsequent career seems to have been devoted 
entirely to ecclesiastical matters, and for the last ten years 
of his life he did not contribute a paper to any scientific 
society. Arago, after a characteristic lament that Brinkley 
should have forsaken the pursuit of science for the 


temporal and spiritual attractions of a bishopric, pays a 
tribute to tbe conscientiousness of the quondam astronomer, 
who would not even allow a telescope to be brought into 
the palace lest his mind should be distracted from his 
sacred duties. 

The good bishop died on the 13th September, 1835. 
He was buried in the chapel of Trinity College, and a fine 
monument to his memory is a familiar object at the foot 
of the noble old staircase of the library. The best memo- 
rial of Brinkley is his admirable book on the " Elements 
of Plane Astronomy." It passed through many editions in 
his lifetime, and even at the present day the same work, 
revised first by Dr. Luby, and more recently by the Rev. 
Dr. Stubbs and Dr. Briinnow, has a large and well- 
merited circulation. 


This illustrious son of an illustrious father was born at 
Slough, near "Windsor, on the 7th March, 1792. He was 
the only child of Sir William Herschel, who had married 
somewhat late in life, as we have already mentioned. 

The surroundings among which the young astronomer 
was reared afforded him an excellent training for that 
career on which he was to enter, and in which he was 
destined to -attain a fame only less brilliant than that of 
his father. The circumstances of his youth permitted him 
to enjoy one great advantage which was denied to the 
elder Herschel. He was able, from his childhood, to 
devote himself almost exclusively to intellectual pursuits. 
William Herschel, in the early part of his career, had 
only been able to snatch occasional hours for study from 
his busy life as a professional musician. But the son, 
having been born with a taste for the student's life, was 
fortunate enough to have been endowed with the leisure 
and the means to enjoy it from the commencement. His 
early years have been so well described by the late Pro- 
fessor Pritchard in the " Report of the Council of the 
Royal Astronomical Society for 1872," that I venture to 
make an extract here : — 


''A. few traits of John Her sch el's boyhood, mentioned 
by himself in his maturer life, have been treasured up by 
those who were dear to him, and the record of some of 
them may satisfy a curiosity as pardonable as inevitable, 
which craves to learn through what early steps great 
men or great nations become illustrious. His home was 
singular, and singularly calculated to nurture into great- 
ness any child born as John Herschel was with natural 
gifts, capable of wide development. At the head of the 
house there was the aged, observant, reticent philosopher, 
and rarely far away his devoted sister, Caroline Herschel, 
whose labours and whose fame are still cognisable as a 
beneficent satellite to the brighter light of her illustrious 
brother. It was in the companionship of these remark- 
able persons, and under the shadow of his father's 
wonderful telescope, that John Herschel passed his boyish 
years. He saw them, in silent but ceaseless industry, 
busied about things which had no apparent concern with 
the world outside the walls of that well-known house, 
but which, at a later period of his life, he, with an un- 
rivalled eloquence, taught his countrymen to appreciate 
as foremost among those living influences which but 
satisfy and elevate the noblest instincts of our nature. 
What sort of intercourse passed between the father and 
the boy may be gathered from an incident or two which 
he narrated as having impressed themselves permanently 
on the memory of his youth. He once asked his father 
what he thought was the oldest of all things. The father 
replied, after the Socratic method, by putting another 
question : * And what do you yourself suppose is the 
oldest of all things ? ' The boy was not successful in his 



Astronometer made "by Sir J. Herschel to compare the light of certain 
stars by the intervention of the moon. 

answers, thereon the old astronomer took up a small 
stone from the garden walk : * There, my child, there is 
the oldest of all the things that I certainly know/ On 
another occasion his father is said to have asked the boy, 
^ What sort of things, do you think, are most alike?' 
The delicate, blue-eyed boy, after a short pause, replied, 
' The leaves of the same tree are most like each other/ 
' Gather, then, a handful of leaves of that tree,' rejoined 
the philosopher, *and choose two that are alike.' The 
boy failed ; but he hid the lesson in his , heart, and his 
thoughts were revealed after many days. These incidents 
may be trifles ; nor should we record them here had not 
John Herschel himself, though singularly reticent about 
his personal emotions, recorded them as having made a 
strong impression on his mind. Beyond all doubt we can 
trace therein, first, that grasp and grouping of many 
things in one, implied in the stone as the oldest of things ; 
and, secondly, that fine and subtle discrimination of each 


thing out of many like things as forming the main 
features which characterized the habit of our venerated 
friend's philosophy." 

John Herschel entered St. John's College, Cambridge, 
when he was seventeen years of age. His university 
career abundantly fulfilled his father's eager desire, that 
his only son should develop a capacity for the pursuit of 
science. After obtaining many lesser distinctions, he 
finally came out as Senior Wrangler in 1813. It was, 
indeed, a notable year in the mathematical annals of the 
University. Second on that list, in which Herschel' s 
name was first, appeared that of the illustrious Peacock, 
afterwards Dean of Ely, who remained throughout life 
one of Herschel's most intimate friends. 

Almost immediately after taking his degree, Herschel 
gave evidence of possessing a special aptitude for original 
scientific investigation. He' sent to the Royal Society a 
mathematical paper which was published in the Philo- 
8opliical Transactions. Doubtless the splendour that 
attached to the name he bore assisted him in procuring an 
early recognition of his own great powers. Certain it is 
that he was made a Fellow of the Eoyal Society at the un- 
precedentedly early age of twenty-one. Even after this 
remarkable encouragement to adopt a scientific career as 
the business of his life, it does not seem that John Her- 
schel at first contemplated devoting himself exclusively to 
science. He commenced to prepare for the profession of 
the Law by entering as a student at the Middle Temple, 
and reading with a practising barrister. 

But a lawyer John Herschel was not destined to become. 
Circumstances brought him into association with some 


leading scientific men. He presently discovered that his 
inclinations tended more and more in the direction of 
purely scientific pursuits. Thus it came to pass that the 
original intention as to the calling which he should follow 
was gradually abandoned. Fortunately for science Her- 
schel found its pursuit so attractive that he was led, as his 
father had been before him, to give up his whole life to 
the advancement of knowledge. Nor was it unnatural 
that a Senior Wrangler, who had once tasted the delights 
of mathematical research, should have been tempted to 
devote much time to this fascinating pursuit. By the 
time John Herschel was twenty-nine he had published 
so much mathematical work, and his researches were con- 
sidered to possess so much merit, that the Royal Society 
awarded him the Copley Medal, which was the highest 
distinction it was capable of conferring. 

At the death of his father in 1822, John Herschel, with 
his tastes already formed for a scientific career, found 
himself in the possession of ample means. To him also 
passed all his father's great telescopes and apparatus. 
These material aids, together with a dutiful sense of filial 
obligation, decided him to make practical astronomy the 
main work of his life. He decided to continue to its 
completion that great survey of the heavens which had 
already been inaugurated, and, indeed, to a large extent 
accomplished, by his father. 

The first systematic piece of practical astronomical work 
which John Herschel undertook was connected with the 
measurement of what are known as " Double Stars." It 
should be observed, that there are in the heavens a number 
of instances in which two stars are seen in very close 


association. In the case of those objects to which the 
expression " Double Stars" is generally applied, the two 
luminous points are so close together that even though 
they might each be quite bright enough to be visible to 
the unaided eye, yet their proximity is such that they 
cannot be distinguished as two separate objects without 
optical aid. The two stars seem fused together into one. 
In the telescope, however, the bodies may be discerned 
separately, though they are frequently so close together 
that it taxes the utmost power of the instrument to in- 
dicate the division between them. 

The appearance presented by a double star might arise 
from the circumstance that the two stars, though really 
separated from each other by prodigious distances, hap- 
pened to lie nearly in the same line of vision, as seen from 
our point of view. No doubt, many of the so-called double 
stars could be accounted for on this supposition. Indeed, 
in the early days when but few double stars were known, 
and when telescopes were not powerful enough to exhibit 
the numerous close doubles which have since been brought 
to light, there seems to have been a tendency to regard all 
double stars as merely such perspective effects. It was 
not at first suggested that there could be any physical 
connection between the components of each pair. The 
appearance presented was regarded as merely due to the 
circumstance that the line joining the two bodies happened 
to pass near the earth. 

In the early part of his career. Sir William Herschel 
seems to have entertained the view then generally held 
by other astronomers with regard to the nature of these 
stellar pairs. The great observer thought that the double 



Sir John Herschel. 

stars could therefore be made to aftord a means of solving 
that problem in wliich so many of the observers of the skies 
had been engaged, namely, the determination of the dis- 
tances of the stars from the earth. Herschel saw that the 
displacement of the earth in its annual movement round 
the sun would produce an apparent shift in the place of 


tlie nearer of the two stars relatively to tlie other, supposed 
to be much, more remote. If this shift could be measured, 
then the distance of the nearer of the stars could be esti- 
mated with some degree of precision. 

As has not unfrequently happened in the history of 
science, an effect was perceived of a very different nature 
from that which had been anticipated. If the relative 
places of the two stars had been apparently deranged 
merely in consequence of the motion of the earth, then 
the phenomenon would be an annual one. After the 
lapse of a year the two stars would have regained their 
original relative positions. This was the effect for which 
William Herschel was looking. In certain of the so- 
called double stars, he, no doubt, did find a movement. 
He detected the remarkable fact that both the apparent 
distance and the relative positions of the two bodies 
were changing. But what was his surprise to observe 
that these alterations were not of an annually periodic 
character. It became evident then that in some cases 
one of the component stars was actually revolving round 
the other, in an orbit which required many years for its 
completion. Here was indeed a remarkable discovery. 
It was clearly impossible to suppose that movements of 
this kind could be mere apparent displacements, arising 
from the annual shift in our point of view, in consequence 
of the revolution of the earth. Herschel' s discovery 
established the interesting fact that, in certain of these 
double stars, or binary stars, as these particular objects 
are more expressively designated, there is an actual 
orbital revolution of a character similar to that which 
the earth performs around the sun. Thus it was demon- 


strated tliat in these particular double stars the nearness 
of the two components was not merely apparent. The 
objects must actually lie close together at a distance 
which is small in comparison with the distance at which 
either of them is separated from the earth. The fact that 
the heavens contain pairs of twin suns in mutual revolu- 
tion was thus brought to light. 

In consequence of this beautiful discovery, the atten- 
tion of astronomers was directed to the subject of double 
stars with a degree of interest which these objects had 
never before excited. It was therefore not unnatural 
that John Herschel should have been attracted to this 
branch of astronomical work. Admiration for his father's 
discovery alone might have suggested that the son should 
strive to develop this territory newly opened up to 
research. But it also happened that the mathematical 
talents of the younger Herschel inclined his inquiries in 
the same direction. He saw clearly that, when sufficient 
observations of any particular binary star had been accu- 
mulated, it would then be within the power of the mathe- 
matician to elicit from those observations the shape and 
the position in space of the path which each of the 
revolving stars described around the other. Indeed, in 
some cases he would be able to perform the astonishing 
feat of determining from his calculations the weight of 
these distant suns, and thus be enabled to compare them 
with the mass of our own sun. 

But this work must follow the observations, it could 
not precede them. The first step was therefore to observe 
and to measure with the utmost care the positions and 
distances of those particular double stars which appear to 



Nebula in Southern Hemi- 
sphere, drawn by Sir John 

offer the greatest promise in 
this particular research. In 
1821, Herschel and a friend of 
his, Mr. James South, agreed to 
work together with this object. 
South was a medical man with 
an ardent devotion to science, 
and possessed of considerable 
wealth. He procured the best 
astronomical instruments that 
money could obtain, and became 
a most enthusiastic astronomer 
and a practical observer of 
tremendous energy. 
South and John Herschel worked together for two 
years m the observation and measurement of the double 
stars discovered by Sir William Herschel. In the course 
of this time their assiduity was rewarded by the accu- 
mulation of so great a mass of careful measurements 
that when published, they formed quite a volume in the 
Thiloso'phical Transactions. The value and accuracy of 
the work, when estimated by standards which form proper 
criteria for that period, is universally recognised. It 
greatly promoted the progress of sidereal astronomy, and 
the authors were in consequence awarded medals from the 
Royal Society, and the Eoyal Astronomical Society, as 
well as similar testimonials from various foreign institu- 

This work must, however, be regarded as merely intro- 
ductory to the main labours of John Herschel's life. 
His father devoted the greater part of his years as an 


observer to wliat he called his " sweeps " of the heavens. 
The great reflecting telescope, twenty feet long, was 
moved slowly up and down through an arc of about two 
degrees towards and from the pole, while the celestial 
panorama passed slowlj^ in the course of the diurnal 
motion before the keenly watching eye of the astronomer. 
Whenever a double star traversed the field Herschel 
described it to his sister Caroline, who, as we have already 
mentioned, was his invariable assistant in his midnight 
watches. When a nebula appeared, then he estimated 
its size and its brightness, he noticed whether it had a 
nucleus, or whether it had stars disposed in any signifi- 
cant manner with regard to it. He also dictated any 
other circumstance which he deemed worthy of record. 
These observations were duly committed to writing by the 
same faithful and indefatigable scribe, whose business it 
also was to take a memorandum of the exact position of 
the object as indicated by a dial placed in front of her 
desk, and connected with the telescope. 

John Herschel undertook the important task of re- 
observing the various double stars and nebulas which had 
been discovered during these memorable vigils. The son, 
however, lacked one inestimable advantage which had 
been possessed by the father. John Herschel had no 
assistant to discharge all those duties which Caroline had 
so efficiently accomplished. He had, therefore, to modify 
the system of sweeping previously adopted in order to 
enable all the work both of observing and of recording to 
be done by himself. ThiS; in many ways, was a great 
drawback to the work of the younger astronomer. The 
division of labour between the observer and the 8crib§ 


enables a greatly increased quantity of work to be got 
througb. It is also distinctly disadvantageous to an 
observer to bave to use bis eye at tbe telescope directly 
after be bas been employing it for reading tbe gradua- 
tions on a circle, by tbe ligbt of a lamp, or for entering 
memoranda in a note book. Nebulee, especially, are often 
so excessively faint tbat tbey can only be properly ob- 
served by an eye wbicb is in tbat bigbly sensitive condi- 
tion wbicb is obtained by long continuance in darkness. 
Tbe frequent witbdrawal of tbe eye from tbe dark field 
of tbe telescope, and tbe application of it to reading by 
artificial ligbt, is very prejudicial to its use for tbe more 
delicate purpose. Jobn Herscbel, no doubt, availed bim- 
self of every precaution to mitigate tbe ill effects of tbis 
inconvenience as mucb as possible, but it must bave told 
upon bis labours as compared witb tbose of bis fatber. 

But nevertbeless Jobn Herscbel did great work during 
bis *' sweeps.'* He was specially particular to note all 
tbe double stars wbicb presented tbemselves to bis obser- 
vation. Of course some little discretion must be allowed 
in deciding as to wbat degree of proximity in adjacent 
stars does actually bring tbem witbin tbe category of 
" double stars." Sir Jobn set down all sucb objects as 
seemed to bim likely to be of interest, and tbe results of 
bis discoveries in tbis brancb of astronomy amount to 
some tbousands. Six or seven great memoirs in tbe 
Transactions of tbe Royal Astronomical Society bave been 
devoted to giving an account of bis labours in tbis 
department of astronomy. 

One of tbe acbievements by wbicb Sir Jobn Herscbel 
is best known is bis invention of a metbod by wbicb 


the orbits of binary stars could be determined. It will be 
observed that when one star revolves around another in 
consequence of the law of gravitation, the orbit described 
must be an ellipse. This ellipse, however, generally 
speaking, appears to us more or less foreshortened, for it 

Tlie cluster in the Centaur, drawn by Sir John Herschel. 

Is easily seen that only under highly exceptional circum- 
stances would the plane in which the stars move happen 
to be directly square to the line of view. It therefore 
follows that what we observe is not exactly the track of 
one star around the other ; it is rather the projection of 
that track as seen on the surface of the skv. JN^ow it is 
remarkable that this apparent path Is still an ellipse. 
Herschel contrived a very ingenious and simple method 
by which he could discover from the observations the size 
and position of the ellipse in which the revolution actually 


takes place. He showed how, from the study of the 
apparent orbit of the star, and from certain measurements 
which could easily be effected upon it, the determination 
of the true ellipse in which the movement is performed 
could be arrived at. In other words, Herschel solved in 
a beautiful manner the problem of finding the true orbits 
of double stars. The importance of this work may be 
inferred from the fact that it has served as the basis on 
which scores of other investigators have studied the fasci- 
nating subject of the movement of binary stars. 

The labours, both in the discovery and measurement of 
the double stars, and in the discussion of the observations 
with the object of finding the orbits of such stars as are 
in actual revolution, received due recognition in yet 
another gold medal awarded by the Eoyal Society. An 
address was delivered on the occasion by the Duke of 
Sussex (30th November, 1833), in the course of which, 
after stating that the medal had been conferred on Sir 
John Herschel, he remarks : — 

" It has been said that distance of place confers the 
same privilege as distance of time, and I should gladly 
avail myself of the privilege which is thus afforded me by 
Sir John Herschel' s separation from his country and 
friends, to express my admiration of his character in 
stronger terms than I should otherwise venture to use ; 
for the language of panegyric, however sincerely it may 
flow from the heart, might be mistaken for that of flattery, 
if it could not thus claim somewhat of an historical charac- 
ter ; but his great attainments in almost every department of 
human knowledge, his fine powers as a philosophical writer, 
bis great services and his distinguished devotion to soienoe, 


the high principles which have regulated his conduct in 
every relation of life, and, above all, his engaging modesty, 
which is the crown of all his other virtues, presenting 
such a model of an accomplished philosopher as can rarely 
be found beyond the regions of fiction, demand abler pens 
than mine to describe them in adequate terms, however 
much inclined I might feel to undertake the task.'' 

The first few lines of the eulogium just quoted allude 
to Herschel's absence from England. This was not 
merely an episode of interest in the career of Herschel, 
it was the occasion of one of the greatest scientific expedi- 
tions in the whole history of astronomy. 

Herschel had, as we have seen, undertaken a revision 
of his father's ** sweeps '* for new objects, in those skies 
which are visible from our latitudes in the northern 
hemisphere. He had well-nigh completed this task. 
Zone by zone the whole of the heavens which could be 
observed from Windsor had passed under his review. He 
had added hundreds to the list of nebulae discovered by 
his father. He had announced thousands of double stars. 
At last, however, the great survey was accomplished. 
The contents of the northern hemisphere, so far at least 
as they could be disclosed by his telescope of twenty feet 
focal length, had been revealed. 

But Herschel felt that this mighty task had to be sup- 
plemented by another of almost equal proportions, before 
it could be said that the twenty-foot telescope had done 
its work. It was only the northern half of the celestial 
sphere which had been fully explored. The southern half 
was almost virgin territory, for no other astronomer was 
possessed of a telescope of such power as those which the 



'^L \'€\j^ 

Sir John Herschel's Observatory at FelcHiausen, Cape of Good Hope. 

Herschels liad used. It is true, of course, that as a 
certain margin of the southern hemisphere was visible 
from these latitudes, it had been more or less scrutinized 
by observers in northern skies. And the glimpses which 
had thus been obtained of the celestial objects in the 
southern sky, were such as to make an eager astronomer 
long for a closer acquaintance with the celestial wonders 
of the south. The most glorious object in the sidereal 
heavens, the Great Nebula in Orion, lies indeed in that 
southern hemisphere to which the younger Herschel's 
attention now became directed. It fortunately happens, 
however, for votaries of astronomy all the world over, that 
Nature has kindly placed her most astounding object, 


the great Nebula in Orion, in such a favoured position, 
near the equator, that from a considerable range of lati- 
tudes, both north and south, the wonders of the N"ebula 
can be explored. There are grounds for thinking that 
the southern heavens contain noteworthy objects which, 
on the whole, are nearer to the solar system than are the 
noteworthy objects in the northern skies. The nearest 
star whose distance is known. Alpha Centauri, lies in the 
southern hemisphere, and so also does the most splendid 
cluster of stars. 

Influenced by the desire to examine these objects. Sir 
John Herschel determined to take his great telescope to 
a station in the southern hemisphere, and thus complete 
his survey of the sidereal heavens. The latitude of the 
Cape of Good Hope is such that a suitable site could be 
there found for his purpose. The purity of the skies in 
South Africa promised to provide for the astronomer 
those clear nights which his delicate task of surveying 
the nebulae would require. 

On November 13, 1833, Sir John Herschel, who had 
by this time received the honour of knighthood from 
William lY., sailed from Portsmouth for the Cape of Good 
Hope, taking with him his gigantic instruments. After 
a voyage of two months, which was considered to be a fair 
passage in those days, he landed in Table Bay, and having 
duly reconnoitred various localities, he decided to place 
his observatoiy at a place called Feldhausen, about six 
miles from Cape Town, near the base of the Table Moun- 
tain. A commodious residence was there available, and 
in it he settled with his family. A temporary building 
was erected to contain the equatorial, but the great 


twenty-foot telescope was accommodated with no more 
shelter than is provided by the open canopy of heaven. 

As in his earKer researches at home, the attention of 
the great astronomer at the Cape of Good Hope was chiefly 
directed to the measurement of the relative positions 
and distances apart of the double stars, and to the close 
examination of the nebulae. In the delineation of the 
form of these latter objects Herschel found ample employ- 
ment for his skilful pencil. Many of the drawings he has 
made of the celestial wonders in the southern sky are 
admirable examples of celestial portraiture. 

The number of the nebulse and of those kindred objects, 
the star clusters, which Herschel studied in the southern 
heavens, during four years of delightful labour, amount 
in all to one thousand seven hundred and seven. His 
notes on their appearance, and the determinations of 
their positions, as well as his measurements of double 
stars, and much other valuable astronomical research, 
were published in a splendid volume, brought out at the 
cost of the Duke of Northumberland. This is, indeed, a 
monumental work, full of interesting and instructive 
reading for any one who has a taste for astronomy. 

Herschel had the good fortune to be at the Cape on 
the occasion of the periodical return of Halley's great 
comet in 1833. To the study of this body he gave assi- 
duous attention, and the records of his observations form 
one of the most interesting chapters in that remarkable 
volume to which we have just referred. 

Early in 1838 Sir John Herschel returned to England. 
He had made many friends at the Cape, who deeply 
sympathised with his self-imposed labours while he was 



Granite Column at Feldhausen, Cape Town, to commemorate Sir John 
Herschel's survey of the Southern Heavens. 

resident among them. They desired to preserve the recol- 
lection of this visit, which would always, they considered, 
be a source of gratification in the colony. Accordingly, a 
number of scientific friends in that part of the world 
raised a monument with a suitable inscription, on the spot 
which had been occupied by the great twenty-foot reflector 
at Feldhausen. 

His return to England after five years of absence was 
naturally an occasion for much rejoicing among the lovers 
of astronomy. He was entertained at a memorable ban- 
quet, and the Queen, at her coronation, made him a 
baronet. His famous aunt Caroline, at that time aired 
^ig^ty, was still in the enjoyment of her faculties, and 
was able to estimate at its true value the further lustre 
which was added to the name she bore. But there is 


reason to believe tiiat her satisfaction was not quite 
unmixed with other feelings. With whatever favour she 
might regard her nephew^ he was still not the brother to 
whom her life had been devoted. So jealous was this 
vigorous old lady of the fame of the great brother "William, 
that she could hardly hear with patience of the achieve- 
ments of any other astronomer, and this failing existed in 
some degree even when that other astronomer happened 
to be her illustrious nephew. 

With Sir John Herschers survey of the Southern 
Hemisphere it may be said that his career as an observing 
astronomer came to a close. He did not again engage in 
any systematic telescopic research. But it must not be 
inferred from this statement that he desisted from active 
astronomical work. It has been well observed that Sir 
John Herschel was perhaps the only astronomer who has 
studied with success, and advanced by original research, 
every department of the great science with which his 
name is associated. It was to some other branches of 
astronomy besides those concerned with looking through 
telescopes, that the rest of the astronomer^s life was to be 

To the general student Sir John Herschel is best known 
by the volume which he published under the title of 
" Outlines of Astronomy." This is, indeed, a masterly 
work, in which the characteristic difficulties of the subject 
are resolutely faced and expounded with as much sim- 
plicity as their nature will admit. As a literary effort 
this work is admirable, both on account of its picturesque 
language and the ennobling conceptions of the universe 
which it unfolds. The student who desires to become 


acquainted with those recondite departments of astronomy, 
in which the effects of the disturbing action of one planet 
upon the motions of another planet are considered, will 
turn to the chapters in Herschel's famous work on the 
subject. There he will find this complex matter eluci- 
dated, without resort to difficult mathematics. Edition 
after edition of this valuable work has appeared, and 
though the advances of modern astronomy have left some- 
what out of date in certain departments, yet the exposi- 
tions it contains of the fundamental parts of the science 
still remain unrivalled. 

Another great work which Sir John undertook after 
his return from the Cape, was a natural climax to those 
labours on which his father and he had been occupied for 
so many years. We have already explained how the 
work of both these observers had been mainly devoted to 
the study of the nebulae and the star clusters. The results 
of their discoveries had been announced to the world in 
numerous isolated memoirs. The disjointed nature of 
these publications made their use very inconvenient. But 
still it was necessary for those who desired to study the 
marvellous objects discovered by the Herschels, to have 
frequent recourse to the original works. To incorporate 
all the several observations of nebulae into one great 
systematic catalogue, seemed, therefore, to be an indis- 
pensable condition of progress in this branch of know- 
ledge. No one could have been so fitted for this task as 
Sir John Herschel. He, therefore, attacked and carried 
through the great undertaking. Thus at last a grand 
catalogue of nebulae and clusters was produced. JN'ever 
before was there so majestic an inventory. If we remem- 


ber that each of the nebulae is an object so vast, that the 
whole of the solar system would form an inconsiderable 
speck by comparison, what are we to think of a collection 
in which these objects are enumerated in thousands ? In 
this great catalogue we find arranged in systematic order 
all the nebulae and all the clusters which had been 
revealed by the diligence of the Herschels, father and 
son, in the Northern Hemisphere, and of the son alone in 
the Southern Hemisphere. Nor should we omit to men- 
tion that the labours of other astronomers were likewise 
incorporated. It was unavoidable that the descriptions 
given to each of the objects should be very slight. Abbre- 
viations are used, which indicate that a nebula is bright, 
or very bright, or extremely bright, or faint, or very faint, 
or extremely faint. Such phrases have certainly but a 
relative and technical meaning in such a catalogue. The 
nebulae entered as extremely bright by the experienced 
astronomer are only so described by way of contrast to 
the great majority of these delicate telescopic objects. 
Most of the nebulae, indeed, are so difficult to see, that 
they admit of but very slight description. It should be 
observed that Herschel's catalogue augmented the number 
of known nebulous objects to more than ten times that 
collected into any catalogue which had ever been compiled 
before the days of William Herschel's observing began. 
But the study of these objects still advances, and the 
great telescopes now in use could probably show at least 
twice as many of these objects as are contained in the list 
of Herschel, of which a new and enlarged edition has 
since been brought out by Dr. Dreyer. 

One of the best illustrations of Sir John Herschel's 


literary powers is to be found in tlie address wliicli he 
delivered at the Hoyal Astronomical Society, on the occa- 
sion of presenting a medal to Mr. Francis Baily, in recog- 
nition of his catalogue of stars. The passage I shall here 
cite places in its proper aspect the true merit of the 
laborious duty involved in such a task as that which Mr. 
Baily had carried through with such success : — 

"If we ask to what end magnificent establishments 
are maintained by states and sovereigns, furnished with 
masterpieces of art, and placed under the direction of men 
of first-rate talent and high-minded enthusiasm, sought 
out for those qualities among the foremost in the ranks of 
science, if we demand cui bono '^ for what good a Bradley 
has toiled, or a Maskelyne or a Piazzi has worn out his 
venerable age in watching, the answer is — not to settle 
mere speculative points in the doctrine of the universe ; 
not to cater for the pride of man by refined inquiries into 
the remoter mysteries of nature ; not to trace the path of 
our system through space, or its history through past and 
future eternities. These, indeed, are noble ends and which 
I am far from any thought of depreciating ; the mind 
swells in their contemplation, and attains in their pursuit 
an expansion and a hardihood which fit it for the boldest 
enterprise. But the direct practical utility of such labours 
is fully worthy of their speculative grandeur. The stars 
are the landmarks of the universe ; and, amidst the endless 
and complicated fluctuations of our system, seem placed 
by its Creator as guides and records, not merely to elevate 
our minds by the contemplation of what is vast, but to 
teach us to direct our actions by reference to what is 
iromi;table iu His works. It is^ indeed, hardlv possibly 


to over- appreciate their value in. this point of view. 
Every well-determined star, from the moment its place is 
registered, becomes to the astronomer, the geographer, 
the navigator, the surveyor, a point of departure which 
can never deceive or fail him, the same for ever and in all 
places, of a delicacy so extreme as to be a test for every 
instrument yet invented by man, yet equally adapted for 
the most ordinary purposes; as available for regulating 
a town clock as for conducting a navy to the Indies ; as 
effective for mapping down the intricacies of a petty 
barony as for adjusting the boundaries of Transatlantic 
empires. When once its place has been thoroughly ascer- 
tained and carefully recorded, the brazen circle with 
which that useful work was done may moulder, the 
marble pillar may totter on its base, and the astronomer 
himself survive only in the gratitude of posterity; but 
the record remains, and transfuses all its own exactness 
into every determination which takes it for a ground- 
work, giving to inferior instruments — nay, even to tem- 
porary contrivances, and to the observations of a few 
weeks or days — all the precision attained originally at 
the cost of so much time, labour, and expense." 

Sir John Herschel wrote many other works besides 
those we have mentioned. His '* Treatise on Meteor- 
ology" is, indeed, a standard work on this subject, and 
numerous articles from the same pen on miscellaneous 
subjects, which have been collected and reprinted, seemed 
as a relaxation from his severe scientific studies. Like 
certain other great mathematicians Herschel was also a 
poet, and he published a translation of the Iliad into 
blank verse. 


In his later years Sir John Herschel lived a retired 
life. For a brief period lie had, indeed, been induced to 
accept the office of Master of the Mint. It was, however, 
evident that the routine of such an occupation was not in 
accordance with his tastes, and he gladly resigned it, to 
return to the seclusion of his study in his beautiful home 
at CoUingwood, in Kent. 

His health having gradually failed, he died on the 11th 
May, 1871, in the seventy-ninth year of his age. 


The subject of our present sketch occupies quite a distinct 
position in scientific history. Unlike many others who 
have risen by their scientific discoveries from obscurity to 
fame, the great Earl of Eosse was himself born in the 
purple. His father, who, under the title of Sir Lawrence 
Parsons, had occupied a distinguished position in the Irish 
Parliament, succeeded on the death of his father to the 
Earldom which had been recently created. The subject 
of our present memoir was, therefore, the third of the 
Earls of Eosse, and he was born in York on June 17, 
1800. Prior to his father's death in 1841, he was known 
as Lord Oxmantown. 

The University education of the illustrious astronomer 
was begun in Dublin and completed at Oxford. We do 
not hear in his case of any very remarkable University 
career. Lord Eosse was, however, a diligent student, and 
obtained a first-class in mathematics. He always took a 
o-reat deal of interest in social questions, and was a pro- 
found student of political economy. He had a seat in the 
House of Commons, as member for King's County, from 
1821 to 1834, his ancestral estate being situated in thisj 
part of Irelaiid. 



The Earl of Eosse, 

Lord BossG was endowed bj nature with a special taste 
for meclianical pursuits. Not only liad lie the qualifi- 
cations of a scientific engineer, but be bad tbe manual 
dexterity wbicb qualified bim personally to carry out 
many practical arts. Xord Kosse was, in fact, a skilful 
mechanic, an experienced founder, and an ingenious 
optician. His acquaintances wera largely among those 
who were iuterested in mechanical pursuits, and it was 



his delight to visit the works or engineering establish- 
ments where refined processes in the arts were being 
carried on. It has often been stated — and as I have been 
told by members of his family, truly stated — that on one 
occasion, after he had been shown over some large works 
in the north of England, the proprietor bluntly said that 
he was greatly in want of a foreman, and would indeed be 
pleased if his visitor, who had evinced such extraordinary 
capacity for mechanical operations, would accept the post. 
Lord Bosse produced his card, and gently explained that 
he was not exactly the right man, but he appreciated the 
compliment, and this led to a pleasant dinner, and was the 
basis of a long friendship. 

I remember on one occasion hearing Lord Rosse explain 
how it was that he came to devote his attention to astro- 
nomy. It appears that when he found himself in the 
possession of leisure and of means, he deliberately cast 
around to think how that means and that leisure could be 
most usefully employed. Nor was it surprising that he 
should search for a direction which would offer special 
scope for his mechanical tastes. He came to the conclu- 
sion that the building of great telescopes was an art which 
had received no substantial advance since the great days 
of William Herschel. He saw that to construct mighty 
instruments for studying the heavens required at once the 
command of time and the command of wealth, while he 
also felt that this was a subject the inherent dijQB.culties of 
which would tax to the uttermost whatever mechanical 
skill he might possess. Thus it was he decided that the 
construction of great telescopes should become the business 
of his life. 



In the centre of Ireland, seventy miles from Dublin, on 
the border between King's County and Tipperary, is a 
little town whereof w^e must be cautious before writing the 
name. The inhabitants of that town frequently insist 
that its name is Birr,* while the official designation is 
Parsonstown, and to this day for every six people who 
apply one name to the town, there will be half a dozen 
who use the other. But whichever it may be, Birr or 
Parsonstown — and I shall generally call it by the latter 
name— it is a favourable specimen of an Irish county 
own. The widest street is called the Oxmantown Mall. 
It is bordered by the dwelling-houses of the chief resi- 
dents, and adorned with rows of stately trees. At one 
end of this distinctly good feature in the town is the 
Parish Church, while at the opposite end are the gates 
leading into Birr Castle, the ancestral home of the house 
of Parsons. Passing through the gates the visitor enters 

* Considering tlie fame acquired by Parsonstown from Lord Eosse's 
mirrors, it may be interesting to note the following extract from ' ' The 
Natural History of Ireland," by Br. Gerard Boate, Thomas MoUneux, 
M.D., P.R.S., and others, which shows that 150 years ago Parsonstown 
was famous for its glass : — ' ' We shall conclude this chapter with the glass, 
there having been several glasshouses set up by the English in Ireland, 
none in Dublin or other cities, but all of them in the country ; amongst 
which the principal was that of Birre, a market town, otherwise called 
Parsonstown, after one Sir Lawrence Parsons, who, having purchased 
that lordship, built a goodly house upon it ; his son William Parsons 
having succeeded him in the possession of it ; which town is situate in 
Queen's County, about fifty miles (Irish) to the south-west of Dublin, 
upon the borders of the two provinces of Leinster and Munster ; from 
this place Dublin was furnished with all sorts of window and drinking 
glasses, and such other as commonly are in use. One part of the mate- 
rials, viz., the sand, they had out of England; the other, to wit the 
ashes, they made in the place of ash-tree, and used no other. The 
chiefest difficulty was to get the clay for the pots to melt the materials 
in ; this they had out of the north."— Chap. XXI.y Sect. VIII., '' Of the 
Glass made in Ireland." 








a spacious demesne, possessing mucL. beauty of wood and 
water, one of the most pleasing features being tbe junc- 
tion of the two rivers, which, unite at a spot ornamented 
by beautiful timber. At various points illustrations of 
the engineering skill of the great Earl will be observed. 
The beauty of the park has been greatly enhanced by the 
construction of an ample lake, designed with the consum- 
mate art by which art is concealed. Even in mid-summer 
it is enlivened by troops of wild ducks preening them- 
selves in that confidence which they enjoy in those happy 
localities where the sound of a gun is seldom heard. The 
water is led into the lake by a tube which passes under 
one of the two rivers just mentioned, while the overflow 
from the lake turns a water-wheel, which works a pair 
of elevators ingeniously constructed for draining the low- 
lying parts of the estate. 

Birr Castle itself is a noble mansion with reminis- 
cences from the time of Cromwell. It is surrounded by a 
moat and a drawbridge of modern construction, and from 
its windows beautiful views can be had over the varied 
features of the park. But while the visitors to Parsons- 
town will look with great interest on this residence of an 
Irish landlord, whose delight it was to dwell in his own 
country, and among his own people, yet the feature which 
they have specially come to observe is not to be found in the 
castle itself. On an extensive lawn, sweeping down from 
the moat towards the lake, stand two noble masonry walls. 
They are turreted and clad with ivy, and considerably 
loftier than any ordinary house. As the visitor approaches, 
he will see between those walls what may at first sight 
appear to him to be the funnel of a steamer lying down 


horizontally. On closer approach he will find that it is an 
immense wooden tube, sixty feet long, and upwards of six 
feet in diameter. It is in fact large enough to admit of a 
tall man entering into it and walking erect right through 
from one end to the other. This is indeed the most 
ffio-antic instrument which has ever been constructed for 
the purpose of exploring the heavens. Closely adjoin- 
ing the walls between which the great tube swings, is a 
little building called *' The Observatory." In this the 
smaller instruments are contained, and there are kept 
the books which are necessary for reference. The obser- 
vatory also offers shelter to the observers, and provides 
the bright fire and the cup of warm tea, which are so 
acceptable in the occasional intervals of a night's observa- 
tion passed on the top of the walls with no canopy but the 
winter sky. 

Almost the first point which would strike the visitor to 
Lord Eosse's telescope is that the instrument at which he 
is looking is not only enormously greater than anything 
of the kind that he has ever seen before, but also that 
it is something of a totally different nature. In an ordi- 
nary telescope he is accustomed to find a tube with lenses 
of glass at either end, while the large telescopes that we 
see in our observatories are also in general constructed on 
the same principle. At one end there is the object-glass, 
and at the other end the eye-piece, and of course it is 
obvious that with an instrument of this construction it is 
to the lower end of the tube that the eye of the observer 
must be placed when the telescope is pointed to the skies. 
But in Lord Eosse's telescope you would look in vain for 
these glasses, and it is not at the lower end of the instru- 


ment that you are to take your station when you are going 
to make your observations. The astronomer at Parsonstown 
has rather to avail himself of the ingenious system of 
staircases and galleries, by which he is enabled to obtain 
access to the mouth of the great tube. The colossal telescope 
which swings between the great walls, like Herschel's great 
telescope already mentioned, is a reflector, the original in- 
vention of which is due of course to Newton. The optical 
work which is accomplished by the lenses in the ordinary 
telescope is effected in the type of instrument constructed 
by Lord Eosse by a reflecting mirror which is placed at 
the lower end of the vast tube. The mirror in this instru- 
ment is made of a metal consisting of two parts of copper 
to one of tin. As we have already seen, this mixture 
forms an alloy of a very peculiar nature. The copper and 
the tin both surrender their distinctive qualities, and unite 
to form a material of a very different physical character. 
The copper is tough and brown, the tin is no doubt silvery 
in hue, but soft and almost fibrous in texture. When the 
two metals are mixed together in the proportions I have 
stated, the alloy obtained is intensely hard and quite brittle, 
being in both these respects utterly unlike either of the 
two ingredients of which it is composed. It does, how- 
ever, resemble the tin in its whiteness, but it acquires a 
lustre far brighter than tin ; in fact, this alloy hardly falls 
short of silver itself in its brilliance when polished. 

The first duty that Lord Eosse had to undertake was 
the construction of this tremendous mirror, six feet across, 
and about four or five inches thick. The dimensions were 
far in excess of those which had been contemplated in 
any previous attempt of the same kind. Ilerschel had no 














doubt fashioned one mirror of four feet in diameter, and 
many others of smaller dimensions, but the processes 
which he employed had never been fully published, and 
it was obvious that, with a large increase in dimensions, 
great additional difficulties had to be encountered. Diffi- 
culties began at the very commencement of the process, 
and were experienced in one form or another at every 
subsequent stage. In the first place, the mere casting of 
a great disc of this mixture of tin and copper, weighing 
something like three or four tons, involved very trouble- 
some problems. No doubt a casting of this size, if the 
material had been, for example, iron, would have offered 
no difficulties beyond those with which every practical 
founder is well acquainted, and which he has to encounter 
daily in the course of his ordinary work. But speculum 
metal is a material of a very intractable description. 
There is, of course, no practical difficulty in melting the 
copper, nor in adding the proper proportion of tin when 
the copper has been melted. There may be no great 
difficulty in arranging an organisation by which several 
crucibles, filled with the molten material, shall be poured 
simultaneously so as to obtain the requisite mass of metal, 
but from this point the difficulties begin. For speculum 
metal when cold is excessively brittle, and were the 
casting permitted to cool like an ordinary copper or iron 
casting, the mirror would inevitably fly into pieces. Lord 
Hosse, therefore, found it necessary to anneal the casting 
with extreme care by allowing it to cool very slowly. 
This was accomplished by drawing the disc of metal as 
soon as it had entered into the solid state, though still 
glowing red, into an annealing oven. There the tem- 


perature was allowed to subside so gradually, tliat six 
weeks elapsed before the mirror had reached the tempera- 
ture of the external air. The necessity for extreme pre- 
caution in the operation of annealing will be manifest if 
we reflect on one of the accidents which happened. On a 
certain occasion, after the cooling of a great casting had 
been completed, it was found, on withdrawing the speculum, 
that it was cracked into two pieces. This mishap was 
eventually traced to the fact that one of the walls of the 
oven had only a single brick in its thickness, and that 
therefore the heat had escaped more easily through that 
side than through the other sides which were built of 
double thickness. The speculum had, consequently, not 
cooled uniformly, and hence the fracture had resulted. 
Undeterred, however, by this failure, as well as by not a 
few other difficulties, into a description of which we cannot 
now enter. Lord E-osse steadily adhered to his self-imposed 
task, and at last succeeded in casting two perfect discs on 
which to commence the tedious processes of grinding and 
polishing. The magnitude of the operations involved may 
perhaps be appreciated if I mention that the value of 
the mere copper and tin entering into the composition 
of each of the mirrors was about £500. 

In no part of his undertaking was Lord Rosse's 
mechanical ingenuity more taxed than in the devising of 
the mechanism for carrying out the delicate operations of 
grinding and polishing the mirrors, whose casting we 
have just mentioned. In the ordinary operations of 
the telescope-maker, such processes had hitherto been 
generally effected by hand, but, of course, such methods 
became impossible when dealing with mirrors which were 


as large as a good-sized dinner table, and wliose weight 
was measured by tons. The rough grinding was effected 
by means of a tool of cast iron about the same size as the 
mirror, which was moved by suitable machinery both 
backwards and forwards, and round and round, plenty of 
sand and water being supplied between the mirror and the 
tool to produce the necessary attrition. As the process 
proceeded and as the surface became smooth, emery was 
used instead of sand ; and when this stage was complete, 
the grinding tool was removed and the polishing tool was 
substituted. The essential part of this was a surface 
of pitch, which, having been temporarily softened by 
heat, was then placed on the mirror, and accepted from 
the mirror the proper form. Eouge was then introduced 
as the polishing powder, and the operation was continued 
about nine hours, by which time the great mirror had 
acquired the appearance of highly polished silver. When 
completed, the disc of speculum metal was about six feet 
across and four inches thick. The depression in the 
centre was about half an inch. Mounted on a little truck, 
the great speculum was then conveyed to the instrument, 
to be placed in its receptacle at the bottom of the tube, 
the length of which was sixty feet, this being the focal 
distance of the mirror. Another small reflector was 
inserted in the great tube sideways, so as to direct the 
gaze of the observer down upon the great reflector. Thus 
was completed the most colossal instrument for the 
exploration of the heavens which the art of man has ever 

It was once my privilege to be one of those to whom 
the illustrious builder of the great telescope entrusted 











its use. For two seasons in 1865 and 1866 I had 
the honour of being Lord Rosse^s astronomer. During 
that time I passed many a fine night in the observer's 
gallery, examining different objects in the heavens with 
the aid of this remarkable instrument. At the time 
I was there, the objects principally studied were the 
nebulssj those faint stains of light which lie on the back- 
ground of the sky. Lord Hosse's telescope was specially 
suited for the scrutiny of these objects, inasmuch as their 
delicacy required all the light-grasping power which could 
be provided. 

One of the greatest discoveries made by Lord Hosse, 
when his huge instrument was first turned towards 
the heavens, consisted in the detection of the spiral 
character of some of the nebulous forms. When the 
extraordinary structure of these objects was first an- 
nounced, the discovery was received with some degree 
of incredulity. Other astronomers looked at the same 
objects, and when they failed to discern — and they 
frequently did fail to discern — the spiral structure which 
Lord Rosse had indicated, they drew the conclusion that 
this spiral structure did not exist. They thought it must 
be due possibly to some instrumental defect or to the 
imagination of the observer. It was, however, hardly 
possible for any one who was both willing and competent 
to examine into the evidence, to doubt the reality of Lord 
Hosse's discoveries. It happens, however, that they 
have been recently placed beyond all doubt by testimony 
which it is impossible to gainsay. A witness never 
influenced by imagination has now come forward, and the 
infallible photographic plate has justified Lord E-osse. 


Among the remarkable discoveries which Dr. Isaac 
Eoberts has recently made in the application of his 
photographic apparatus to the heavens, there is none 
more striking than that which declares, not only that 
the nebula} which Lord Rosse described as spirals, actually 
do possess the character so indicated, but that there are 
many others of the same description. He has even 
brought to light the astonishingly interesting fact that 
there are invisible objects of this class which have never 
been seen by human eye, but whose spiral character is. 
visible to the peculiar delicacy of the photographic tele- 

In his earlier years. Lord Eosse himself used to be 
a diligent observer of the heavenly bodies with the 
great telescope which was completed in the year 1845. 
But I think that those who knew Lord Eosse well, will 
agree that it was more the mechanical processes incidental 
to the making of the telescope which engaged his interest 
than the actual observations with the telescope when it 
was completed. Indeed one who was well acquainted with 
him believed Lord Eosse' s special interest in the great 
telescope ceased when the last nail had been driven into 
it. But the telescope was never allowed to lie idle, for 
Lord Eosse always had associated with him some ardent 
young astronomer, whose delight it was to employ to the 
uttermost the advantages of his position in exploring the 
wonders of the sky. Among those who were in this 
capacity in the early days of the great telescope, I may 
mention my esteemed friend Dr. Johnston Stoney. 

Such was the renown of Lord Eosse himself, brought 
about by his consummate mechanical genius and his 


astronomical discoveries, and such, tlie interest wliicli 
gathered around the marvellous workshops at Birr Castle, 
wherein his monumental exhibitions of optical skill were 
constructed, that visitors thronged to see him from all 
parts of the world. His home at Parsonstown became 
one of the most remarkable scientific centres in Great 
Britain; thither assembled from time to time all the 
leading men of science in the country, as well as many 
illustrious foreigners. For many years Lord Rosse filled 
with, marked distinction the exalted position of President 
of the E,oyal Society, and his advice and experience 
in practical mechanical matters were always at the 
disposal of those who sought his assistance. Personally 
and socially Lord Hosse endeared himself to all with 
whom he came in contact. I remember one of the 
attendants telling me that on one occasion he had the mis- 
fortune to let fall and break one of the small mirrors on 
which Lord Rosse had himself expended many hours of 
hard personal labour. The only remark of his lordship 
was that "accidents will happen.'^ 

The latter years of his life Lord Rosse passed in com- 
parative seclusion ; he occasionally went to London for a 
brief sojourn during the season, and he occasionally went 
for a cruise in his yacht ; but the greater part of the 
year he spent at Birr Castle, devoting himself largely to 
the study of political and social questions, and rarely 
going outside the walls of his demesne, except to church 
on Sunday mornings. He died on October 31, 1867. 

He was succeeded by his eldest son, the present Earl of 
Rosse, who has inherited his father's scientific abilities, 
and done much notable work with the great telescope. 


In our sketch of the life of Flamsteed, we have referred 
to the circumstances under which the famous Observatory 
that crowns Greenwich Hill was founded. We have also 
had occasion to mention that among the illustrious suc- 
cessors of Flamsteed both Halley and Bradley are to be 
included. But a remarkable development of Greenwich Ob- 
servatory from the modest establishment of early days took 
place under the direction of the distinguished astronomer 
whose name is at the head of this chapter. By his labours 
this temple of science was organised to such a degree of 
perfection that it has served [in many respects as a model 
for other astronomical establishments in various parts of 
the world. An excellent account of Airy's career has 
been given by Professor H. H. Turner, in the obituary 
notice published by the Royal Astronomical Society. To 
this I am indebted for many of the particulars here to be 
set down concerning the life of the illustrious Astronomer 

The family from which Airy took his origin came from 
Kentmere, in Westmoreland. His father, William Airy^ 
belonged to a Lincolnshire branch of the same stock. His 
mother's maiden name was Ann Biddell, and her family 



resided at Playford, near Ipswich. William Airy lield 
some small government post wliicli necessitated an occa- 
sional change of residence to different parts of the 
country, and thus it was that his son, George Biddell, 
came to be born at Alnwick, on 27th July, 1801. The 
boy's education, so far as his school life was concerned, 
was partly conducted at Hereford and partly at Colchester. 
He does not, however, seem to have derived much benefit 
from the hours which he passed in the schoolroom. But 
it was delightful to him to spend his holidays on the farm 
at Playford, where his uncle, Arthur Biddell, showed him 
much kindness. The scenes of his early youth remained 
dear to Airy throughout his life, and in subsequent years 
he himself owned a house at Playford, to which it was his 
special delight to resort for relaxation during the course 
of his arduous career. In spite of the defects of his school 
training he seems to have manifested such remarkable 
abilities that his uncle decided to enter him in Cambridge 
University. He accordingly joined Trinity College as a 
sizar in 1819, and after a brilliant career in mathematical 
and physical science he graduated as Senior Wrangler in 
1823. It may be noted as an exceptional circumstance 
that, notwithstanding the demands on his time in study- 
ing for his tripos, he was able, after his second term of 
residence, to support himself entirely by taking private 
pupils. In the year after he had taken his degree he was 
elected to a Fellowship at Trinity College. 

Having thus gained an independent position. Airy 
immediately entered upon that career of scientific work 
which he prosecuted without intermission almost to the 
very close of his life. One of his most interesting 

AIRY. 291 

researches in these early days is on the subject of 
Astigmatism, which defect he had discovered in his own 
eyes. His investigations led him to suggest a means of 
correcting this defect by using a pair of spectacles with 
lenses so shaped as to counteract the derangement which 
the astigmatic eye impressed upon the rays of light. His 
researches on this subject were of a very complete cha- 
racter, and the principles he laid down are to the present 
day practically employed by oculists in the treatment of 
this malformation. 

On the 7th of December, 1826, Airy was elected 
to the Lucasian Professorship of Mathematics in the 
IJniversity of Cambridge, the chair which Newton's occu- 
pancy had rendered so illustrious. His tenure of this 
oflBce only lasted for two years, when he exchanged it 
for the Plumian Professorship. The attraction which led 
him to desire this change is doubtless to be found in the 
circumstance that the Plumian Professorship of Astronomy 
carried with it at that time the appointment of director 
of the new astronomical observatory, the origin of which 
must now be described. 

Those most interested in the scientific side of University 
life decided in 1820 that it would be proper to found an 
astronomical observatory at Cambridge. Donations were 
accordingly sought for this purpose, and upwards of 
£6,000 were contributed by members of the University 
and the public. To this sum £5,000 were added by a 
grant from the University chest, and in 1824 further 
sums amounting altogether to £7,115 were given by the 
University for the same object. The regulations as to 
the administration of the new observatory placed it under 


the management of tlie Plumian Professor, who was to be 
provided with two assistants. Their duties were to consist 
in making meridian observations of the sun, moon, and 
the stars, and the observations made each year were to be 
printed and published. The observatory was also to be 
used in the educational work of the University, for it was 
arranged that smaller instruments were to be provided by 
which students could be instructed in the practical art of 
making astronomical observations. 

The building of the Cambridge Astronomical Observa- 
tory was completed in 1824, but in 1828, when Airy 
entered on the discharge of his duties as Director, 
the establishment was still far from completion, in so far 
as its organisation was concerned. Airy commenced his 
work so energetically that in the next year after his 
appointment he was able to publish the first volume of the 
" Cambridge Astronomical Observations," notwithstanding 
that every part of the work, from the making of the 
observations to the revising of the proof- sheets, had to be 
done by himself. 

It may here be remarked that these early volumes of 
the publications of the Cambridge Observatory contained 
the first exposition of those systematic methods vjf 
astronomical work which Airy afterwards developed to 
such a great extent at Greenwich, and which have been 
subsequently adopted in many other places. No more 
profitable instruction for the astronomical beginner can be 
found than that which can be had by the study of these 
volumes, in which the Plumian Professor has laid down 
with admirable clearness the true principles on which 
meridian work should be conducted. 



Sir George Airy. 
{From a photograph by Mr. U. P. Adams, Greemvich.) 

Airy gradually added to the instruments with which 
the observatory was originally equipped. A mural circle 
was mounted in 1832, and in the same year a small 
equatorial was erected by Jones. This was made use of 
by Airy in a well-known series of observations of Jupiter's 
fourth satellite for the determination of the mass of the 
great planet. His memoir on this subject fully ex- 
pounds the method of finding the weight of a planet from 


observations of the movements of a satellite by which the 
planet is attended. This is, indeed, a valuable investigation 
which no student of astronomy can afford to neglect. The 
ardour with which Airy devoted himself to astronomical 
studies may be gathered from a remarkable report on the 
progress of astronomy during the present century, which 
he communicated to the British Association at its second 
meeting in 1832. In the early years of his life at Cam- 
bridge his most famous achievement was connected with a 
research in theoretical astronomy for which consummate 
mathematical power was required. We can only give a 
brief account of the subject, for to enter into any full 
detail with regard to it would be quite out of the question. 
Yenus is a planet of about the same size and the same 
weight as the earth, revolving in an orbit with lies within 
that described by our globe. Venus, consequently, takes 
less time than the earth to accomplish one revolution round 
the sun, and it happens that the relative movements of 
Yenus and the earth are so proportioned that in the time 
in which our earth accomplishes eight of her revolutions 
the other planet will have accomplished almost exactly 
thirteen. It, therefore, follows that if the earth and 
Yenus are in line with the sun at one date, then in eight 
years later both planets will again be found at the same 
points in their orbits. In those eight years the earth has 
gone round eight times, and has, therefore, regained its 
original position, while in the same period Yenus has 
accomplished thirteen complete revolutions, and, therefore, 
this planet also has reached the same spot where it was at 
first. Yenus and the earth, of course, attract each other, 
and in consequence of these mutual attractions the earth 

AIRY, 295 

is swayed from the elliptic track whicli it would otherwise 
pursue. In like manner Venus is also forced by the 
attraction of the earth to revolve in a track which deviates 
from that which it would otherwise follow. Owing to 
the fact that the sun is of such preponderating magnitude 
(being, in fact, upwards of 300,000 times as heavy as 
either Venus or the earth), the disturbances induced in the 
motion of either planet, in consequence of the attraction 
of the other, are relatively insignificant to the main con- 
trolling agency by which each of the movements is 
governed. It is, however, possible under certain circum- 
stances that the disturbing effects produced upon one 
planet by the other can become so multiplied as to produce 
peculiar effects which attain measurable dimensions. 
Suppose that the periodic times in which the earth and 
Venus revolved had no simple relation to each other, 
then the points of their tracks in which the two planets 
came into line with the sun would be found at different 
parts of the orbits, and consequently the disturbances 
would to a great extent neutralise each other, and produce 
but little appreciable effect. As, however, Venus and the 
earth come back every eight years to nearly the same 
positions at the same points of their track, an accumulative 
effect is produced. For the disturbance of one planet 
upon the other will, of course, be greatest when those two 
planets are nearest, that is, when they lie in line with the 
sun and on the same side of it. Every eight years a 
certain part of the orbit of the earth is, therefore, dis- 
turbed by the attraction of Venus with peculiar vigour. 
The consequence is that, owing to the numerical relation 
between the movements of the planets to which I have 


referred, disturbing effects become appreciable wbicb 
would otherwise be too small to permit of recognition. 
Airy proposed to himself to compute the effects which 
Yenus would have on the movement of the earth in con- 
sequence of the circumstance that eight revolutions of the 
one planet required almost the same time as thirteen 
revolutions of the other. This is a mathematical inquiry 
of the most arduous description, but the Plumian Pro- 
fessor succeeded in working it out, and he had, accord- 
ingly, the gratification of announcing to the E-oyal Society 
that he had detected the influence which Yenus was thus 
able to assert on the movement of our earth around the 
sun. This remarkable investigation gained for its author 
the gold medal of the Royal Astronomical Society in the 
year 1832. 

In consequence of his numerous discoveries, Airy's 
scientific fame had become so well recognised that the 
Government awarded him a special pension, and in 1835, 
when Pond, who was then Astronomer Royal, resigned, 
Airy was offered the post at Greenwich. There was, in 
truth, no scientific inducement to the Plumian Professor 
to leave the comparatively easy post he held at Cambridge, 
in which he had ample leisure to devote himself to those 
researches which specially interested him, and accept that 
of the much more arduous observatory at Greenwich. 
There were not even pecuniary inducements to make the 
change ; however, he felt it to be his duty to accede to 
the request which the Government had made that he 
would take up the position which Pond had vacated, and 
accordingly Airy went to Greenwich as Astronomer Royal 
on October 1st, 1835. 



He immedicately began with his usual energy to organise 
the systematic conduct of the business of the National 
Observatory. To realise one of the main characteristics 
of Airy's great work at Greenwich, it is necessary to 
explain a point that might not perhaps be understood 
without a little explanation by those who have no prac- 
tical experience in an observatory. In the work of an 
establishment such as Greenwich, an observation almost 
always consists of a measurement of some kind. The 
observer may, for instance, be making a measurement of 
the time at which a star passes across a spider line 
stretched through the field of view ; on another occasion 
his object may be the measurement of an angle which 
is read off by examining through a microscope the lines of 
division on a graduated circle when the telescope is so 
pointed that the star is placed on a certain mark in the 
field of view. In either case the immediate result of the 
astronomical observation is a purely numerical one, but it 
rarely happens, indeed we may say it never happens, that 
the immediate numerical result which the observation 
gives expresses directly the quantity which we are really 
seeking for. No doubt the observation has been so 
designed that the quantity we want to find can be obtained 
from the figures which the measurement gives, but the 
object sought is not those figures, for there are always a 
multitude of other influences by which those figures are 
affected. For example, if an observation were to be per- 
fect, then the telescope with which the observation is 
made should be perfectly placed in the exact position 
which it ought to occupy; this is, however, never the 
case, for no mechanic can ever construct or adjust a teles- 


cope SO perfectly as the wants of the astronomer demand. 
The clock also by which we determine the time of the 
observation should be correct, but this is rarely if ever the 
case. We have to correct our observations for such errors, 
that is to say, we have to determine the errors in the 
positions of our telescopes and the errors in the going of 
our clocks, and then we have to determine what the obser- 
vations would have been had our telescopes been abso- 
lutely perfect, and had our clocks been absolutely correct. 
There are also many other matters which have to be 
attended to in order to reduce our observations so as to 
obtain from the figures as yielded to the observer at the 
telescope the actual quantities which it is his object to 

The work of effecting these reductions is gener- 
ally a very intricate and laborious matter, so that it 
has not unfrequently happened that while observations 
have accumulated in an observatory, yet the tedious 
duty of reducing these observations has been allowed to 
fall into arrear. When Airy entered on his duties at 
Grreenwich he iv;und there an enormous mass of observa- 
tions which, though implicitly containing materials of the 
greatest value to astronomers, were, in their unreduced 
form, entirely unavailable for any useful purpose. He, 
therefore, devoted himself to coping with the reduction of 
the observations of his predecessors. He framed systematic 
methods by which the reductions were to be effected, and 
he so arranged the work that little more than careful atten- 
tion to numerical accuracy would be required for the con- 
duct of the operations. Encouraged by the Admiralty, for 
it is under this department that Greenwich Observatory is 

AIRY. 299 

placed, the Astronomer Royal employed a large force of 
computers to deal with the work. By his energy and 
admirable organisation he managed to reduce an extremely 
valuable series of planetary observations, and to publish 
the results, which have been of the greatest importance to 
astronomical investigation. 

The Astronomer Royal was a capable, practical engineer 
as well as an optician, and he presently occupied himself 
by ^designing astronomical instruments of improved 
pattern, which should replace the antiquated instruments 
he found in the observatory. In the course of years 
the entire equipment underwent a total transformation. 
He ordered a great meridian circle, every part of 
which may be said to have been formed from his own 
designs. He also designed the mounting for a fine equa- 
torial telescope worked by a driving clock, which he had 
himself invented. Gradually the establishment at Green- 
wich waxed great under his incessant care. It was the 
custom for the observatory to be inspected every year by a 
board of visitors, whose chairman was the President of the 
Royal Societ}^ At each annual visitation, held on the first 
Saturday in June, the visitors received a report from the 
Astronomer Royal, in which he set forth the business 
which had been accomplished during the past year. It 
was on these occasions that applications were made to the 
Admiralty, either for new instruments or for developing 
the work of the observatory in some other way. After 
the more ofiicial business of the inspection w^as over, the 
observatory was thrown open to visitors, and hundreds of 
people enjoyed on that day the privilege of seeing the 
national observatory. These annual gatherings are 


happily still continued, and tlie first Saturday in June is 
known to be the occasion of one of the most interesting 
reunions of scientific men .which takes place in the course 
of the year. 

Airy's scientific work was, however, by no means confined 
to the observatory. He interested himself largely in 
expeditions for the observation of eclipses and in projects 
for the measurement of arcs on the earth. He devoted much 
attention to the collection of magnetic observations from 
various parts of the world. Especially will it be remem- 
bered that the circumstances of the transits of Yenus, 
which occurred in 1874 and in 1882, were investigated 
by him, and under his guidance expeditions were sent 
forth to observe the transits from those localities in 
remote parts of the earth where observations most suitable 
for the determination of the sun's distance from the 
earth could be obtained. The Astronomer Royal also 
studied tidal phenomena, and he rendered great service 
to the country in the restoration of the standards of length 
and weight which had been destroyed in the great fire at 
the House of Parliament in October, 1834. In the most 
practical scientific matters his advice was often sought, 
and was as cheerfully rendered. IN^ow we find him engaged 
in an investigation of the irregularities of the compass in 
iron ships, with a view to remedying its defects ; now we 
find him reporting on the best gauge for railways. Among 
the most generally useful developments of the observa- 
tory must be mentioned the telegraphic method for the 
distribution of exact time. By arrangement with the 
Post Office, the astronomers at Greenwich despatch each 
morning a signal from the observatory to London at ten 

AIRY. 301 

o'clock precisely. By special apparatus, this signal is 
thence distributed automatically oyer the country, so as to 
enable the time to be known everywhere accurately to a 
single second. It was part of the same system that 
a time ball should be dropped daily at one o'clock at Deal, 
as well as at other places, for the purpose of enabling 
shij^'s chronometers to be regulated. 

Airy's writings were most voluminous, and no fewer 
than forty-eight memoirs by him are mentioned in the 
"Catalogue of Scientific Memoirs," published by the 
Royal Society up to the year 1873, and this only included 
ten years out of an entire life of most extraordinary 
activity. Many other subjects besides those of a purely 
scientific character from time to time engaged his atten- 
tion. He wrote, for instance, a very interesting treatise 
on the Eoman invasion of Britain, especially with a view 
of determining the port from which Ca3sar set forth from 
Gaul, and the point at which he landed on the British 
coast. Airy was doubtless led to this investigation by his 
study of the tidal j^henomena in the Straits of Dover. 
Perhaps the Astronomer Royal is best known to the 
general reading public by his excellent lectures on astro- 
nomy, delivered at the Ipswich Museum in 1848. This 
book has passed through many editions, and it gives a 
most admirable account of the manner in which the 
fundamental problems in astronomy have to be attacked. 
' As years rolled by almost every honour and dis- 
tinction that could be conferred upon a scientific man 
was awarded to Sir George Airy. He was, indeed, the 
recipient of other honours not often awarded for scientific 
distinction. Among these we may mention that in 1875 


lie received the freedom of the City of London, '' as a 
recognition of his indefatigable labours in astronomy, and 
of his eminent services in the advancement of practical 
science, whereby he has so materially benefited the cause 
of commerce and civilisation." 

Until his eightieth year Airy continued to discharge his 
labours at Greenwich with unflagging energy. At last, 
on August 15th, 1881, he resigned the office which he 
had held so long with such distinction to himself and such 
benefit to his country. He had married in 1830 the 
daughter of the Rev. Richard Smith, of Edensor. Lady 
Airy died in 1875, and three sons and three daughters 
survived him. One daughter is the wife of Dr. Routh, 
of Cambridge, and his other daughters were the constant 
companions of their father during the declining years of 
his life. Up to the age of ninety he enjoyed perfect 
physical health, but an accidental fall which then occurred 
was attended with serious results. He died on Saturday, 
January 2nd, 1892, and was buried in the churchyard at 


William Eowan Hamilton was born at midnight be- 
tween the 3rd and 4th of August, 1805, at Dublin, in the 
house which was then 29, but subsequently 36, Dominick 
Street. His father, Archibald Hamilton, was a solicitor, 
and William was the fourth of a family of nine. With 
reference to his descent, it may be sufficient to notice that 
his ancestors appear to have been chiefly of gentle Irish 
families, but that his maternal grandmother was of Scot- 
tish birth. When he was about a year old, his father 
and mother decided to hand over the education of the 
child to his uncle, James Hamilton, a clergyman of Trim, 
in County Meath. James Hamilton's sister, Sydney, 
resided with him, and it was in their home that the days 
of William's childhood were passed. 

In Mr. Graves' '' Life of Sir William Rowan Hamil- 
ton " a series of letters will be found, in which Aunt 
Sydney details the progress of the boy to his mother in 
Dublin. Probably there is no record of an infant pro- 
digy more extraordinary than that which these letters 
contain. At three years old his aunt assured the mother 
that William is " a hopeful blade," but at that time it 
was his physical vigour to which she apparently referred ; 
for the proofs of his capacity, which she adduces, related 


to his prowess in making boys older than himself fly 
before him. In the second letter, a month later, we hear 
that William is brought in to read the Bible for the pur- 
pose of putting to shame other boys double his age who 
could not read nearly so well. Uncle James appears to 
have taken much pains with William's schooling, but his 
aunt said that " how he picks up everything is astonish- 
ing, for he never stops playing and jumping about." When 
he was four years and three months old, we hear that he 
went out to dine at the vicar's, and amused the company 
by reading for them equally well whether the book was 
turned upside down or held in any other fashion. His 
aunt assures the mother that " Willie is a most sensible 
little creature, but at the same time has a great deal of 
roguery." At four years and five months old he came up 
to pay his mother a visit in town, and she writes to her 
sister a description of the boy : — 

*' His reciting is astonishing, and his clear and accurate 
knowledge of geography is beyond belief ; he even draws 
the countries with a pencil on paper, and will cut them 
out, though not perfectly accurate, yet so well that any- 
body knowing the countries could not mistake them ; but 
you will think this nothing when I tell you that he reads 
Latin, Greek, and Hebrew.'' 

Aunt Sydney recorded that the moment Willie got 
back to Trim he was desirous of at once resuming his 
former pursuits. He would not eat his breakfast till his 
uncle had heard him his Hebrew, and he comments on 
the importance of proper pronunciation. At five he 
was taken to see a friend, to whom he repeated long 
passages from Dry den. A gentleman present, who was 


not unnaturally sceptical about Willie's attainments, 
desired to test him in Grreek, and took down a copy of 
Homer which hap^jened to have the contracted type, and 
to his amazement Willie went on with the greatest ease. 
At six years and nine months he was translating Homer 
and Yirgil ; a year later his uncle tells us that Wil- 
liam finds so little difficulty in learning French and 
Italian, that he wishes to read Homer in French. He is 
enraptured with the Iliad, and carries it about with him, 
repeating from it whatever particularly pleases him. At 
eight years and one month the boy was one of a party 
who visited the Scalp in the Dublin mountains, and he 
was so delighted with the scenery that he forthwith deli- 
vered an oration in Latin. At nine years and six months 
he is not satisfied until he learns Sanscrit ; three months 
later his thirst for the Oriental languages is unabated, 
and at ten years and four months he is studying Arabic 
and Persian. When nearly twelve he prepared a manu- 
script ready for publication. It was a "Syriac Grammar," 
in Syriac letters and characters compiled from that of 
Buxtorf, by William Hamilton, Esq., of Dublin and Trim. 
When he was fourteen, the Persian ambassador, Mirza 
Abul Hassan Khan, paid a visit to Dublin, and, as a prac- 
tical exercise in his Oriental languages, the young scholar 
addressed to his Excellency a letter in Persian ; a transla- 
tion of which production is given by Mr. Graves. When 
William was fourteen he had the misfortune to lose 
his father; and he had lost his mother two years pre- 
viously. The boy and his three sisters were kindly 
provided for by different members of the family on both 



It was when William was about fifteen that his atten- 
tion began to be turned towards scientific subjects. These 
were at first regarded rather as a relaxation from the lin- 
guistic studies with which he had been so largely occu- 
pied. On November 22nd, 1820, he notes in his journal 
that he had begun Kewton's '' Principia " ; he commenced 
also the study of astronomy by observing eclipses, occul- 
tations, and similar phenomena. When he was sixteen 
we learn that he had read conic sections, and that he was 
engaged in the study of pendulums. After an attack of 
illness, he was moved for change to Dublin, and in May, 
1822, we find him reading the differential calculus and 
Laplace's " Mecanique Celeste." He criticises an impor- 
tant part of Laplace's work relative to the demonstration 
of the parallelogram of forces. In this same year ap- 
peared the first gushes of those poems which afterwards 
flowed in torrents. 

His somewhat discursive studies had, however, now to 
give place to a more definite course of reading in prepara- 
tion for entrance to the University of Dublin. The tutor 
under whom he entered, Charles Boyton, was himself a dis- 
tinguished man, but he frankly told the young William 
that he could be of little use to him as a tutor, for his pupil 
was quite as fit to be his tutor. Eliza Hamilton, by whom 
this is recorded, adds, " But there is one thing which 
Boyton would promise to be to him, and that was o, friend ; 
and that one proof he would give of this should be that, 
if ever he saw William beginning to be vpset by the sen- 
sation he would excite, and the notice he would attract, 
he would tell him of it." At the beginning of his college 
career he distanced all his competitors in every intel- 


lectual pursuit. At his first term examination in the 
University he was first in Classics and first in Mathe- 
matics, while he received the Chancellor's prize for a 
poem on the Ionian Islands, and another for his poem 
on Eustace de St. Pierre. 

There is abundant testimony that Hamilton had '^a 
heart for friendship formed." Among the warmest of 
the friends whom he made in these early days was 
the gifted Maria Edgeworth, who writes to her sister 
about " young Mr. Hamilton, an admirable Crichton of 
eighteen, a real prodigy of talents, who Dr. Brinkley 
says may be a second Newton, quiet, gentle, and simple." 
His sister Eliza, to whom he was affectionately attached, 
writes to him in 1824 : — 

" I had been drawing pictures of you in my mind in 
your study at Cumberland Street with 'Xenophon,' &c., 
on the table, and you, with your most awfully sublime 
face of thought, now sitting down, and now walking 
about, at times rubbing your hands with an air of satis- 
faction, and at times bursting forth into some very heroical 
strain of poetry in an unknown language, and in your 
own internal solemn ventriloquist-like voice, when you 
address yourself to the silence and solitude of your own 
room, and indeed, at times, even when your mysterious 
poetical addresses are not quite unheard." 

This letter is quoted because it refers to a circumstance 
which all who ever met with Hamilton, even in his latest 
years, will remember. He was endowed with two dis- 
tinct voices, one a high treble, the other a deep bass, and 
he alternately employed these voices not only in ordinary 
conversation, but when he was delivering an address on 


tlie profunditieg of Quaternions to the Royal Irlsli Aca- 
demy, or on similar occasions. His friends had long 
grown so familiar with this peculiarity that they were 
sometimes rather surprised to find how ludicrous it 
appeared to strangers. 

Hamilton was fortunate in finding, while still at a very 
early age, a career open before him which was worthy of 
his talents. He had not ceased to be an undergraduate 
before he was called to fill an illustrious chair in his Uni- 
versity. The circumstances are briefly as follows. 

We have already mentioned that, in 1826, Brinkley 
was appointed Bishop of Cloyne, and the professorship 
of astronomy thereupon became vacant. Such was Hamil- 
ton's conspicuous eminence that, notwithstanding he was 
still an undergraduate, and had only just completed 
his twenty-first year, he was immediately thought 
of as a suitable successor to the chair. Indeed, so 
remarkable were his talents in almost every direction, 
that had the vacancy been in the professorship of classics 
or of mathematics, of English literature or of meta- 
physics, of modern or of Oriental languages, it seems 
difiicult to suppose that he would not have occurred to 
every one as a possible successor. The chief ground, how- 
ever, on which the friends of Hamilton urged his appoint- 
ment was the earnest of original power which he had 
already shown in a research on the theory of Systems of 
Bays. This profound work created a new branch of optics, 
and led a few years later to a superb discovery, by which 
the fame of its author became world-wide. 

At first Hamilton thought it would be presumption 
for him to apply for so exalted a position ; he accord- 


ingly retired to tlie country, and resumed his studies 
for liis degree. Other eminent candidates came for- 
ward, among them some from Cambridge, and a few 
of the Fellows from Trinity College, Dublin, also sent in 
their claims. It was not until Hamilton received an 
urgent letter from his tutor Boyton, in which he was 
assured of the favourable disposition of the Board towards 
his candidature, that he consented to come forward, and 
on June 16th, 1827, he was unanimously chosen to suc- 
ceed the Bishop of Cloyne as Professor of Astronomy in 
the University. The appointment met with almost uni- 
versal approval. It should, however, be noted that 
Brinkley, whom Hamilton succeeded, did not concur in 
the general sentiment. JN^o one could have formed a 
higher opinion than he had done of Hamilton's transcen- 
dent powers ; indeed, it was on that very ground that he 
seemed to view the appointment with disapprobation. He 
considered that it would have been wiser for Hamilton to 
have obtained a Fellowship, in which capacity he would 
have been able to exercise a greater freedom in his choice 
of intellectual pursuits. The bishop seems to have 
thought, and not without reason, that Hamilton's genius 
would rather recoil from much of the routine work of an 
astronomical establishment. Now that Hamilton's whole 
life is before us, it is easy to see that the bishop was entirely 
wrong. It is quite true that Hamilton never became a 
skilled astronomical observer ; but the seclusion of the 
observatory was eminently favourable to those gigantic 
labours to which his life was devoted, and which have 
shed so much lustre, not only on Hamilton himself, but 
also on his University and his country. 


In his early years at Dunsink, Hamilton did make some 
attempts at a practical use of tlie telescopes, but lie pos- 
sessed no natural aptitude for such, work, while the 
exposure which it involved seems to have acted in- 
juriously on his health. He, therefore, gradually allowed 
his attention to be devoted to those mathematical researches 
in which he had already given such promise of distinction. 
Although it was in pure mathematics that he ultimately 
won his greatest fame, yet he always maintained, and 
maintained with justice, that he had ample claims to the 
title of an astronomer. In his later years he set forth 
this position himself in a rather striking manner. De 
Morgan had written commending to Hamilton's notice 
Grant's "History of Physical Astronomy.'' After 
becoming acquainted with the book, Hamilton writes to 
his friend as follows : — 

'' The book is very valuable, and very creditable to its 
composer. But your humble servant may be pardoned if 
he finds himself somewhat amused at the title, * History 
of Physical Astronomy from the Earliest Ages to the 
Middle of the Nineteenth Century,' when he fails to 
observe any notice of the discoveries of Sir W. P. Hamil- 
ton in the theory of the ' Dynamics of the Heavens.' " 

The intimacy between the two correspondents will 
account for the tone of this letter ; and, indeed, Hamilton 
supplies in the lines which follow ample grounds for his 
complaint. He tells how Jacobi spoke of him in Manchester 
in 1842 as " le Lagrange de votre pays," and how Donkin 
had said that, '' The Analytical Theory of Dynamics as it 
exists at present is due mainly to the labours of Lagrange, 
Poisson, Sir W. P. Hamilton, and Jacobi, whose researches 


on this subject present a series of discoveries hardly- 
paralleled for their elegance and importance in any 
other branch of mathematics.'' In the same letter Hamil- 
ton also alludes to the success which had attended the 
applications of his methods in other hands than his own 
to the elucidation of the difficult subject of Planetary 
Perturbations. Even had his contributions to science 
amounted to no more than these discoveries, his tenure of 
the chair would have been an illustrious one. It happens, 
however, that in the gigantic mass of his intellectual work 
these researches, though intrinsically of such importance, 
assume what might almost be described as a relative 

The most famous achievement of Hamilton's earlier 
3^ears at the observatory was the discovery of conical 
refraction. This was one of those rare events in the history 
of science, in which a sagacious calculation has predicted 
a result of an almost startling character, subsequently 
confirmed by observation. At once this conferred on the 
young professor a world-wide renown. Indeed, though 
he was still only twenty- seven, he had already lived 
through an amount of intellectual activity which would 
have been remarkable for a man of threescore and ten. 

Simultaneously with his growth in fame came the 
growth of his several friendships. There were, in the 
first place, his scientific friendships with Herschel, Pobin- 
son, and many others with whom he had copious corres- 
pondence. In the excellent biography to which I have 
referred, Hamilton's correspondence with Coleridge may be 
read, as can also the letters to his lady correspondents, among 
them being Maria Edge worth, Lady Dun raven, and Lady 


Campbell. Many of these sheets relate to literary matters, 
but they are largely intermingled with genial pleasantry, 
and serve at all events ta show the affection and esteem 
with which he was regarded by all who had the privilege 
of knowing him. There are also the letters to the sisters 
whom he adored, letters brimming over with such exalted 
sentiment, that most ordinary sisters would be tempted to 
receive them with a smile in the excessively improbable 
event of their still more ordinary brothers attempting to 
pen such effusions. There are also indications of letters 
to and from other young ladies who from time to time 
w^ere the objects of Hamilton's tender admiration. We 
use the plural advisedly, for, as Mr. Graves has set forth, 
Hamilton's love affairs pursued a rather troubled course. 
The attention which he lavished on one or two fair ones 
was not reciprocated, and even the intense charms of 
mathematical discovery could not assuage the pangs which 
the disappointed lover experienced. At last he reached 
the haven of matrimony in 1833, when he was married to 
Miss Bayly. Of his married life Hamilton said, many 
years later to De Morgan, that it was as happy as he ex- 
pected, and happier than he deserved. He had two sons, 
"William and Archibald, and one daughter, Helen, who 
became the wife of Archdeacon O'Regan. 

The most remarkable of Hamilton's friendships in his 
early years was unquestionably that with Wordsworth. 
It commenced with Hamilton's visit to Keswick ; and on 
the first evening, when the poet met the young mathe- 
matician, an incident occurred which showed the mutual 
interest that was aroused. Hamilton thus describes it in 
a letter to his sister Eliza : — 


Sir W. Bowan Hamilton. 

*' He (Wordsworth.) walked back with our party as far 
as their lodge, and then, on our bidding Mrs. Harrison 
good-night, I offered to walk back with him while my 
party proceeded to the hotel. This offer he accepted, and 
our conversation had become so interesting that when we 
had arrived at his home, a distance of about a mile, he 
proposed to walk back with me on my way to Ambleside, 
a proposal which you may be sure I did not reject ; ^o far 


from it tliat when he came to turn once more towards his 
home I also turned once more along with him. It was 
very late when I reached the hotel after all this walking." 

Hamilton also submitted to Wordsworth an original 
poem, entitled "It Haunts me Yet." The reply of 
Wordsworth is worth repeating : — 

" With a safe conscience I can assure you that, in my 
judgment, your yerses are animated with the poetic spirit, 
as they are evidently the product of strong feeling. The 
sixth and seventh stanzas affected me much, even to the 
dimming of my eyes and faltering of my voice while I was 
reading them aloud. Having said this, I have said 
enough. Now for the j!9er contra. You will not, I am 
sure, be hurt when I tell you that the workmanship (what 
else could be expected from so young a writer ?) is not 
what it ought to be. . . . 

** My household desire to be remembered to you in no 
formal way. Seldom have I parted — never, I was going 
to say — with one whom after so short an acquaintance I 
lost sisrht of with more rearret. I trust we shall meet 


The further affectionate intercourse between Hamilton 
and Wordsworth is fully set forth, and to Hamilton's 
latest years a recollection of his " Rydal hours " was 
carefully treasured and frequently referred to. AYords- 
worth visited Hamilton at the observatory, where a beau- 
tiful shady path in the garden is to the present day 
spoken of as *' Wordsworth \s Walk." 

It was the practice of Hamilton to produce a sonnet on 
almost every occasion which admitted of poetical treat- 
ment, and it was his delight to communicate his verses to 


Ills friends all round. When Whewell was producing his 
"Bridgewater Treatises," he writes to Hamilton in 
1833 :— 

" Your sonnet which you showed me expressed much 
better than I could express it the feeling with which I 
tried to write this book, and I once intended to ask your 
permission to prefix the sonnet to my book, but my friends 
persuaded me that I ought to tell my story in my own 
prose, however much better your verse might be." 

The first epoch-marking contribution to Theoretical 
Dynamics after the time of IN^ewton was undoubtedly 
made by Lagrange, in his discovery of the general 
equations of Motion. The next great step in the same 
direction was that taken by Hamilton in his discovery of 
a still more comprehensive method. Of this contribution 
Hamilton writes to Whewell, March 31st, 1834 : — 

" As to my late paper, a day or two ago sent off to 
London, it is merely mathematical and deductive. I ven- 
tured, indeed, to call the * Mecanique Analy tique ' of 
Lagrange, * a scientific poem ' ; and spoke of Dynamics, 
or the Science of Force, as treating of * Power acting by 
Law in Space and Time.' In other respects it is as un- 
poetical and unmetaphysical as my gravest friends could 

It mav well be doubted whether there is a more beauti- 
ful chapter in the whole of mathematical philosophy than 
that which contains Hamilton's dynamical theory. It is 
disfigured by no tedious complexity of symbols ; it con- 
descends not to any particular problems ; it is an all- 
embracing theory, which gives an intellectual grasp of the 
most appropriate method for discovering the result of the 


application of force to matter. It is tlie very generality 
of this doctrine witich. has somewhat impeded the applica- 
tions of which it is susceptible. The exigencies of exa- 
minations are partly responsible for the fact that the 
method has not become more familiar to students of the 
higher mathematics. An eminent professor has complained 
that Hamilton's essay on dynamics was of such an ex- 
tremely abstract character, that he found himself unable 
to extract from it problems suitable for his examination 

The following extract is from a letter of Professor 
Sylvester to Hamilton, dated 20th of September, 1841. It 
will show how his works were appreciated by so consum- 
mate a mathematician as the writer : — 

^' Believe me, sir, it is not the least of my regrets in 
quitting this empire to feel that I forego the casual occa- 
sion of meeting those masters of my art, yourself chief 
amongst the number, whose acquaintance, whose conversa- 
tion, or even notice, have in themselves the power to inspire, 
and almost to impart fresh vigour to the understanding, 
and the courage and faith without which the efforts of in- 
vention are in vain. The golden moments I enjoyed under 
your hospitable roof at Dunsink, or moments such as they 
were, may probably never again fall to my lot. 

" At a vast distance, and in an humble eminence, I still 
promise myself the calm satisfaction of observing your 
blazing course in the elevated regions of discovery. Such 
national honour as you are able to confer on your country 
is, perhaps, the only species of that luxury for the rich (I 
mean what is termed one's glory) which is not bought at 
the expense of the comforts of the million." 


The study of metaphysics was always a favourite recrea- 
tion when Hamilton sought for a change from the pursuit 
of mathematics. In the year 1834 we find him a diligent 
student of Kant ; and, to show the views of the author of 
Quaternions and of Algebra as the Science of Pure Time on 
the " Critique of the Pure E/Cason/' we quote the following 
letter, dated 18th of July, 1834, from Hamilton to Vis- 
count Adare : — 

'* I have read a large part of the ' Critique of the Pure 
Peason,' and find it wonderfully clear, and generally 
quite convincing. ISTotwithstanding some previous pre- 
paration from Berkeley, and from my own thoughts, I 
seem to have learned much from Kant's own statement of 
his views of ' Space and Time.' Yet, on the whole, a 
large part of my pleasure consists in recognising throuo-h 
Kant's works, opinions, or rather views, which have been 
long familiar to myself, although far more clearly and 

systematically expressed and combined by him 

Kant is, I think, much more indebted than he owns, or, 
perhaps knows, to Berkeley, whom he calls by a sneer, 
* gutem Berkeley ' .... as it were, ' good soul, well- 
meaning man,' who was able for all that to shake to its 
centre the world of human thought, and to effect a revo- 
lution among the early consequences of which was the 
growth of Kant himself." 

At several meetings of the British Association Hamil- 
ton was a very conspicuous figure. Especially was this 
the case in 1835, when the Association met in Dublin, and 
when Hamilton, though then but thirty years old, had 
attained such celebrity that even among a very brilliant 
gathering his name was perhaps the most renowned. A 


banquet was given at Trinity College in honour of the 
meeting. The distinguished visitors assembled in the 
library of the University. ^ The Earl of Mulgrave, then 
Lord Lieutenant of Ireland, made this the opportunity of 
conferring on Hamilton the honour of knighthood, grace- 
fully adding, as he did so : *' I but set the royal, and 
therefore the national mark, on a distinction already 
acquired by your genius and labours.'* 

'' The banquet followed," writes Mr. Graves. " It was no 
little addition to the honour Hamilton had already received 
that, when Professor Whewell returned thanks for the 
toast of the University of Cambridge, he thought it 
appropriate to add the words, ' There was one point which 
strongly pressed upon him at that moment : it was now 
one hundred and thirty years since a great man in another 
Trinity College knelt down before his sovereign, and rose 
up Sir Isaac Newton.' The compliment was welcomed by 
immense applause." 

A more substantial recognition of the labours of Hamil- 
ton took place subsequently. He thus describes it in a 
letter to Mr. Graves of 14th of November, 1843 : — 

'* The Queen has been pleased — and you will not doubt 
that it was entirely unsolicited, and even unexpected, on 
my part — ' to express her entire approbation of the grant 
of a pension of two hundred pounds per annum from the 
Civil List ' to me for scientific services. The letters from 
.Sir Eobert Peel and from the Lord Lieutenant of Ireland, 
in which this grant has been communicated or referred to, 
have been really more gratifying to my feelings than the 
addition to my income, however useful, and almost neces- 
sary, that may have been." 



The circumstances we have mentioned might lead to the 
supposition that Hamilton was then at the zenith of his 
fame, but this was not so. It might more truly be said, 
that his achievements up to this point were rather the 
preliminary exercises which fitted him for the gigantic 
task of his life. The name of Hamilton is now chiefly 
associated with his memorable invention of the calculus of 
Quaternions. It was to the creation of this branch of 
mathematics that the maturer powers of his life were 
devoted; in fact he gives us himself an illustration of how 
completely habituated he became to the new modes of 
thought which Quaternions originated. In one of his 
later years he happened to take up a copy of his famous 
paper on Dynamics, a paper which at the time created such 
a sensation among mathematicians, and which is at this 
moment regarded as one of the classics of dynamical 
literature. He read, he tells us, his paper with consider- 
able interest, and expressed his feelings of gratification 
that he found himself still able to follow its reasoning with- 
out undue effort. But it seemed to him all the time as a work 
belonging to an age of analysis now entirely superseded. 
In order to realise the magnitude of the revolution 
which Hamilton has wrought in the application of sj^mbols 
to mathematical investigation, it is necessary to think of 
what Hamilton did beside the mighty advance made by 
Descartes. To describe the character of the quaternion 
calculus would be unsuited to the pages of this work, but 
we may quote an interesting letter, written by Hamilton 
from his deathbed, twenty- two years later, to his son 
Archibald, in which he has recorded the circumstances of 
the discovery • — ^ 


" Indeed, I happen to be able to put tbe finger of memory 
upon the year and month — October, 1843 — when, haying 
recently returned from visits to Cork and Parsonstown, 
connected with a meeting of the British Association, the 
desire to discover the laws of multiplication referred to, 
reo-ained with me a certain strength and earnestness which 
had for years been dormant, but was then on the point of 
beino- gratified, and was occasionally talked of with you. 
Every morning in the early part of the above-cited month, 
on my coming down to breakfast, your (then) little brother, 
William Edwin, and yourself, used to ask me, ' Well, 
papa, can you multiply triplets ?' Whereto I was always 
obliged to reply, with a sad shake of the head : * JNTo, I 
can only add and subtract them.' 

"But on the 16th day of the same month— which hap- 
pened, to be Monday, and a Council day of the Royal 
Irish Academy — I was walking in to attend and preside, 
and your mother was walking with me along the Royal 
Canal, to which she had perhaps driven ; and although she 
talked with me now and then,, yet an undercurrent of 
thought was going on in my mind which gave at last a 
result, whereof it is not too much to say that I felt at once 
the importance. An electric circuit seemed to close ; and a 
spark flashed forth the herald (as I foresaw immediately) of 
many long years to come of definitely directed thought 
and work by myself, if spared, and, at all events, on the 
part of others if I should even be allowed to live long 
enough distinctly to communicate the discovery. Nor 
could I resist the impulse — unphilosophical as it may have 
"been — to cut with a knife on a stone of Brougham Bridge, 
as we passed it, the fundamental formula which contains 


the Solution of the Trohlem^ but, of course, the inscription 
has long since mouldered away. A more durable notice 
remains, however, on the Council Books of the Academy 
for that day (October 16, 1843), which records the fact 
that I then asked for and obtained leave to read a Paper 
on * Quaternions,' at the First General Meeting of the 
Session ; which reading took place accordingly, on Monday, 
the 13th of JN^ovember following." 

Writing to Professor Tait, Hamilton gives further 
particulars of the same event. And again in a letter to 
the Rev. J. W. Stubbs :— 

''To-morrow will be the fifteenth birthday of the 
Quaternions. They started into life full-grown on the 
16th October, 1843, as I was walking with Lady Hamilton 
to Dublin, and came up to Brougham Bridge — which my 
boys have since called Quaternion Bridge. I pulled out 
a pocket-book which still exists, and made entry, on 
which at the very moment I felt that it might be worth my 
while to expend the labour of at least ten or fifteen years 
to come. But then it is fair to say that this was because I 
felt a problem to have been at that moment solved, an 
intellectual want relieved which had haunted me for at 
least fifteen years before. 

" But did the thought of establishing such a system, in 
which geometrically opposite facts — namely, two lines (or 
areas) which are opposite in space give always a positive 
product — ever come into anybody's head till I was led to 
it in October, 1843, by trying to extend my old theory of 
algebraic couples, and of algebra as the science of pure 
time ? As to my regarding geometrical addition of lines 
as equivalent to composition of motions (and as performed 


by the same rules), that is indeed essential in my theory, 
but not peculiar to it ; on the contrary, I am only one of 
many who have been led to this view of addition." 

Pilgrims in future ages will doubtless visit the spot 
commemorated by the invention of Quaternions. Perhaps, 
as they look at that by no means graceful structure. 
Quaternion Bridge, they will regret that the hand of 
some Old Mortality had not been occasionally emploj^ed 
in cutting the memorable inscription afresh. It is now 
irrecoverably lost. 

It was ten years after the discovery that the great 
volume appeared under the title of *' Lectures on Quater- 
nions," Dublin, 1853. The reception of this work by the 
scientific world was such as might have been expected, 
from the extraordinary reputation of its author, and the 
novelty and importance of the new calculus. His valued 
friend, Sir John Herschel, writes to him in that style of 
which he was a master : — 

" Now,\uost heartily let me congratulate you on getting 
out your book — on having found utterance, ore rotundo, 
for all that labouring and seething mass of thought which 
has been from time to time sending out sparks, and 
gleams, and smokes, and shaking the soil about you ; but 
now breaks into a good honest eruption, with a lava stream 
and a shower of fertilizing ashes. 

" Metaphor and simile apart, there is work for a twelve- 
month to any man to read such a book, and for half a 
lifetime to digest it, and I am glad to see it brought to a 

We may also record Hamilton's own opinion expressed 
to Humphrey Lloyd : — 


*' In general, although in one sense I hope that I am 
actually growing modest about the quaternions, from my 
seeing so many peeps and vistas into future expansions of 
their principles, I still must assert that this discovery 
appears to me to be as important for the middle of the 
nineteenth century as the discovery of fluxions was for 
the close of the seventeenth." 

Bartholomew Lloyd died in 1837. He had been the 
Provost of Trinity College, and the President of the Royal 
Irish Academy. Three candidates were put forward by 
their respective friends for the vacant Presidency. One 
was Humphrey Lloyd, the son of the late Provost, and 
the two others were Hamilton and Archbishop Whately. 
Lloyd from the first urged strongly the claims of Hamil- 
ton, and deprecated the putting forward of his own name. 
Hamilton in like manner desired to withdraw in favour of 
Lloyd. The wish was strongly felt by many of the 
Fellows of the College that Lloyd should be elected, \w. 
consequence of his having a more intimate association 
with collegiate life than Hamilton; while his scientific 
eminence was world-wide. The election ultimately gave 
Hamilton a considerable majority over Lloyd, behind 
whom the Archbishop followed at a considerable distance. 
All concluded happily, for both Lloyd and the Archbishop 
expressed, and no doubt felt, the pre-eminent claims of 
Hamilton, and both of them cordially accepted the oflice 
of a Yice-President, to which, according to the constitu- 
tion of the Academy, it is the privilege of the incoming 
President to nominate. 

In another chapter I have mentioned as a memorable 
episode in astronomical history, that Sir J. Herschel went 


for a prolonged sojourn to the Cape of Good Hope, for the 
purpose of submitting the southern skies to the same 
scrutiny with the great telescope that his father had given 
to the northern skies. The occasion of Herschel's return, 
after the brilliant success of his enterprise, was celebrated 
by a banquet. On June 15th, 1838, Hamilton was 
assigned the high honour of proposing the health of 
Herschel. This banquet is otherwise memorable in 
Hamilton's career as being one of the two occasions in 
which he was in the company of his intimate friend De 

In the year 1838 a scheme was adopted by the E-oyal 
Irish Academy for the award of medals to the authors of 
papers which appeared to possess exceptionally high merit. 
At the institution of the medal two papers were named in 
competition for the prize. One was Hamilton's " Memoir 
on Algebra, as the Science of Pure Time." The other was 
MacuUagh's paper on the *' Laws of Crystalline Eeflec- 
tion and Refraction." Hamilton expresses his gratifica- 
tion that, mainly in consequence of his own exertions, 
he succeeded in having the medal awarded to Macullagh 
rather than to himself. Indeed, it would almost appear 
as if Hamilton had procured a letter from Sir J. Herschel, 
which indicated the importance of Macullagh' s memoir in 
such a way as to decide the issue. It then became Hamil- 
ton's duty to award the medal from the chair, and to 
deliver an address in which he expressed his own sense of 
the excellence of Macullagh' s scientific work. It is the 
more necessary to allude to these points, because in the 
whole of his scientific career it would seem that Macullagh 
was the only man with whom Hamilton had ever even 


an approach to a dispute about priority. The incident 
referred to took place in connection with the discovery of 
conical refraction, the fame of which MacuUagh made a 
preposterous attempt to wrest from Hamilton. This is 
evidently alluded to in Hamilton's letter to the Marquis 
of Northampton, dated June 28th, 1838, in which we 
read : — 

" And though some former circumstances prevented me 
from applying to the person thus distinguished the sacred 
name of friend, I had the pleasure of doing justice .... 
to his high intellectual merits. ... I believe he was not 
only gratified but touched, and may, perhaps, regard me 
in future with feelings more like those which I long to 
entertain towards him.'' 

Hamilton was in the habit, from time to time, of com- 
mencing the keeping of a journal, but it does not appear 
to have been sj^stematically conducted. Whatever diffi- 
culties the biographer may have experienced from its 
imperfections and irregularities, seem to be amply com- 
j)ensated for by the practice which Hamilton had of pre- 
serving copies of his letters, and even of comparatively 
insignificant memoranda. In fact, the minuteness with 
which apparently trivial matters were often noted down 
appears almost whimsical. He frequently made a 
memorandum of the name of the person who carried 
a letter to the post, and of the hour in which it was 
despatched. On the other hand, the letters which he 
received were also carefully preserved in a mighty mass 
of manuscripts, with which his study was encumbered, and 
with which many other parts of the house were not unfre- 
quently invaded. If a letter was laid aside for a few 


hours, it would become lost to view amid the seething 
mass of papers, though occasionally, to use his own ex- 
pression, it might be seen " eddying " to the surface in 
some later disturbance. 

The great volume of " Lectures on Quaternions '' had 
been issued, and the author had received the honours 
which the completion of such a task would rightfully 
bring him. The publication of an immortal work does 
not, however, necessarily provide the means for paying 
the printer's bill. The printing of so robust a volume 
was necessarily costly ; and even if all the copies could be 
sold, which at the time did not seem very likely, they 
would hardly have met the inevitable expenses. The pro- 
vision of the necessary funds was, therefore, a matter for 
consideration. The Board of Trinity College had already 
contributed £200 to the printing, but yet another hundred 
was required. Even the discoverer of Quaternions found 
this a source of much anxiety. However, the Board, 
urged by the representation of Humphrey Lloyd, now one 
of its members, and, as we have already seen, one of 
Hamilton's staunchest friends, relieved him of all lia- 
bility. We may here note that, notwithstanding the 
pension which Hamilton enjoyed in addition to the salary 
of his chair, he seems always to have been in some- 
what straitened circumstances, or, to use his own words 
in one of his letters to De Morgan, " Though not an 
embarrassed man, I am anything rather than a rich one." 
It appears that, notwithstanding the world-wide fame of 
Hamilton's discoveries, the only profit in a pecuniary 
sense that he ever obtained from any of his works was by 
the sale of what he called his Icosian Game. Some enter- 


prising publisher, on the urgent representations of one of 
Hamilton's friends in London, bought the copyright of 
the Icosian Game for £25. Even this little speculation 
proved unfortunate for the purchaser, as the public could 
not be induced to take the necessary interest in the 

After the completion of his great book, Hamilton ap- 
peared for a while to permit himself a greater indulgence 
than usual in literary relaxations. He had copious cor- 
respondence with his intimate friend, Aubrey de Yere, 
and there were multitudes of letters from those troops of 
friends whom it was Hamilton's privilege to possess. He 
had been greatly affected by the death of his beloved sister 
Eliza, a poetess of much taste and feeling. She left to 
him her many papers to preserve or to destroy, but he 
said it was only after the expiration of four years of 
mourning that he took courage to open her pet box of 

The religious side of Hamilton's character is frequently 
illustrated in these letters ; especially is this brought out 
in the correspondence with De Vere, who had seceded 
to the Church of Eome. Hamilton writes, August 4, 
1855 :— 

" If, then, it be painfully evident to both, that under 
such circumstances there cannot (whatever we may both 
desire) be now in the nature of things, or of minds, the 
same degree of intimacy between us as of old ; since we 
could no longer talk with the same degree of unreserve on 
ever?/ subject which happened to present itself, but mtisty 
from the simplest instincts of courtesy, be each on his 
guard not to say what might be offensive, or, at least. 


painful to the other; yet we were once so intimate, and 
retain still, and, as I trust, shall always retain, so much 
of regard and esteem and appreciation for each other, 
made tender by so many associations of my early youth 
and your boyhood, which can never be forgotten by either 
of us, that (as times go) tico or three very respectable 
FRIENDSHIPS might easily be carved out from the frag- 
ments of our former and ever-to-be-remembered intimacy. 
It would be no exaggeration to quote the words : * Heu ! 
quanto minus est cum reliquis versari, quam tui memi- 
nisse ! ' " 

In 1858 a correspondence on the subject of Quaternions 
commenced between Professor Tait and Sir William 
Hamilton. It was particularly gratifying to the discoverer 
that so competent a mathematician as Professor Tait 
should have made himself acquainted with the new cal- 
culus. It is, of course, well known that Professor 
Tait subsequently brought out a most valuable ele- 
mentary treatise on Quaternions, to which those who 
are anxious to become acquainted with the subject will 
often turn in preference to the tremendous works of 

In the year 1861 gratifying information came to hand 
of the progress which the study of Quaternions was 
making abroad. Especially did the subject attract the 
attention of that accomplished mathematician, Moebius, 
who had already in his " Barycentrische Calculus " been 
led to conceptions which bore more affinity to Quaternions 
than could be found in the writings of any other mathe- 
matician. Such notices of his work were always pleasing 
to Hamilton, and they served, perhaps, as incentives to 


that still closer and more engrossing labour by which 
he became more and more absorbed. During the last few 
years of his life he was observed to be even more of a 
recluse than he had hitherto been. His powers of long 
and continuous study seemed to grow with advancing 
years, and his intervals of relaxation, such as they were, 
became more brief and more infrequent. 

It was not unusual for him to work for twelve hours at 
a stretch. The dawn would frequently surprise him as 
he looked up to snufE his candles after a night of fasci- 
nating labour at original research. Regularity in habits 
was impossible to a student who had prolonged fits of what 
he called his mathematical trances. Hours for rest and 
hours for meals could only be snatched in the occasional 
lucid intervals between one attack of Quaternions and the 
next. When hungry, he would go to see whether any- 
thing could be found on the sideboard ; when thirsty, he 
would visit the locker, and the one blemish in the man's 
personal character is that these latter visits were sometimes 
paid too often. 

As an example of one of Hamilton's rare diversions 
from the all-absorbing pursuit of Quaternions, we find 
that he was seized with curiosity to calculate back to the 
date of the Hegira, which he found on the 15th July, 622. 
He speaks of the satisfaction with which he ascertained 
subsequently that Herschel had assigned precisely the 
same date. Metaphysics remained also, as it had ever 
been, a favourite subject of Hamilton's readings and 
meditations and of correspondence with his friends. He 
wrote a very long letter to Dr. Ingleby on the subject of his 
" Introduction to Metaphysics." In it Hamilton alludes, 


as lie has done also in other places, to a peculiarity of his 
own vision. It was habitual to him, by some defect in 
the correlation of his eyes, to see always a distinct image 
with each ; in fact, he speaks of the remarkable effect 
which the use of a good stereoscope had on his sensations 
of vision. It was then, for the first time, that he realised 
how the two images which he had always seen hitherto 
would, under normal circumstances, be blended into one. 
He cites this fact as bearing on the phenomena of 
binocular vision, and he draws from it the inference 
that the necessity of binocular vision for the correct 
appreciation of distance is unfounded. *' I am quite 
sure," he says, "that I see distance with each eye 

The commencement of 1865, the last year of his life, 
saw Hamilton as diligent as ever, and corresponding with 
Salmon and Cayley. On April 26th he writes to a friend 
to say, that his health has not been good for years past, 
and that so much work has injured his constitution ; and 
he adds, that it is not conducive to good spirits to find 
that he is accumulating another heavy bill with the 
printer for the publication of the " Elements." This was, 
indeed, up to the day of his death, a cause for serious 
anxiety. It may, however, be mentioned that the whole 
cost, which amounted to nearly £500, was, like that of 
the previous volume, ultimately borne by the College. 
Contrary to anticipation, the enterprise, even in a 
pecuniary sense, cannot have been a very unprofitable 
one. The whole edition has long been out of print, 
and as much as £5 has since been paid for a single 


It was on the 9tli of May, 1865, that Hamilton was in 
Dublin for the last time. A few days later he had a violent 
attack of gout, and on the 4th of June he became alarm- 
ingly ill, and on the next day had an attack of epileptic 
convulsions. However, he slightly rallied, so that before 
the end of the month he was again at work at the 
*' Elements." A gratifying incident brightened some of 
the last days of his life. The National Academy of Science 
in America had then been just formed. A list of foreign 
Associates had to be chosen from the whole world, and a 
discussion took place as to what name should be placed 
first on the list. Hamilton was informed by private com- 
munication that this great distinction was awarded to him 
by a majority of two-thirds. 

In August he was still at work on the table of contents 
of the '^Elements,'* and one of his very latest efforts was 
his letter to Mr. Gould, in America, communicating his 
acknowledgments of the honour which had been just con- 
ferred upon him by the National Academy. On the 2nd 
of September Mr. Graves went to the observatory, in 
response to a summons, and the great mathematician at 
once admitted to his friend that he felt the end was 
approaching. He mentioned that he had found in the 
14Dth Psalm a wonderfully suitable expression of his 
thoughts and feelings, and he wished to testify his faith 
and thankfulness as a Christian by partaking of the Lord's 
Supper. He died at half-past two on the afternoon of the 
2nd of September, 1865, aged sixty years and one month. 
He was buried in Mount Jerome Cemetery on the 7th of 

Many were the letters and other more public manif esta- 


tions of tlie feelings awakened by Hamilton's death. Sir 
John Herschel wrote to the widow : — 

** Permit me only to add that among the many scientific 
friends whom time has deprived me of, there has been 
none whom I more deeply lament, not only for his splendid 
talents, but for the excellence of his disposition and the 
perfect simplicity of his manners — -so great, and yet so 
devoid of pretensions." 

De Morgan, his old mathematical crony, as Hamilton 
affectionately styled him, also wrote to Lady Hamilton : — - 

'* I have called him one of my dearest friends, and most 
truly ; for I know not how much longer than twenty-five 
years we have been in intimate correspondence, of most 
friendly agreement or disagreement, of most cordial 
interest in each other. And yet we did not know each 
othet's faces. I met him about 1830 at Babbage's break- 
fast table, and there for the only time in our lives we 
conversed. I saw him, a long way off, at the dinner given 
to Herschel (about 1838) on his return from the Cape ; 
and there we were not near enough, nor on that crowded 
day could we get near enough, to exchange a word. And 
this is all I ever saw, and, so it has pleased God, all I 
shall see in this world of a man whose friendly communica- 
tions were among my greatest social enjoyments, and 
greatest intellectual treats." 

There is a very interesting memoir of Hamilton, 
written by De Morgan, in the Gentleman's Magazine 
for 1866, in which he produces an excellent sketch of his 
friend, illustrated by personal reminiscences and anecdotes. 
He alludes, among other things, to the picturesque con- 
fusion of the papers in his study. There was some sort 


of order in the mass, discernible, however, by Hamil- 
ton alone, and any invasion of the domestics, with a 
view to tidying up, would throw the mathematician, 
as we are informed, into " a good honest thundering 

Hardly any two men, who were both powerful mathe- 
maticians, could have been more dissimilar in every other 
respect than were Hamilton and De Morgan. The highly 
poetical temperament of Hamilton was remarkably con- 
trasted with the practical realism of De Morgan. Hamilton 
sends sonnets to his friend, who replies by giving the poet 
advice about making his will. The metaphysical subtle- 
ties, with which Hamilton often filled his sheets, did not 
seem to have the same attraction for De Morgan that he 
found in battles about the quantification of the Predicate. 
De Morgan was exquisitely witty, and though his jokes 
were always appreciated by his correspondent, yet Hamilton 
seldom ventured on anything of the same kind in reply ; 
indeed his rare attempts at humour only produced results 
of the most ponderous description. But never were two 
scientific correspondents more perfectly in sympathy with 
each other. Hamilton's work on Quaternions, his labours 
in Dynamics, his literary tastes, his metaphysics, and his 
poetry, were all heartily welcomed by his friend, whose 
letters in reply invariably evince the kindliest interest in 
all Hamilton's concerns. In a similar way De Mor- 
gan's letters to Hamilton always met with a heartfelt 

Alike for the memory of Hamilton, for the credit of his 
University, and for the benefit of science, let us hope that 
a collected edition of his works will ere long appear — a 


collection which shall show those early achievements in a 
splendid optical theory, those achievements of his more 
mature powers which made him the Lagrange of his 
country, and finally those creations of the Quaternion 
Calculus by which new capabilities have been bestowed on 
the human intellect. 


The name of Le Yerrier is one that goes down to fame on 
account of very different discoveries from those which 
have given renown to several of the other astronomers 
whom we have mentioned. We are sometimes apt to 
identify the idea of an astronomer with that of a man who 
looks through a telescope at the stars; but the word 
astronomer has really much wider significance. JSTo man 
who ever lived has been more entitled to be designated an 
astronomer than Le Yerrier, and yet it is certain that he 
never made a telescopic discovery of any kind. Indeed, 
so far as his scientific achievements have been concerned, 
he might never have looked through a telescope at all. 

For the full interpretation of the movements of the 
heavenly bodies, mathematical knowledge of the most 
advanced character is demanded. The mathematician at 
the outset calls upon the astronomer who uses the instru- 
ments in the observatory, to ascertain for him at various 
times the exact positions occupied by the sun, the moon, 
and the planets. These observations, obtained with the 
greatest care, and purified as far as possible from the 
errors by which they may be affected, form, as it were, 
the raw material on which the mathematician exercises his 


skill. It is for him to elicit from the observed places 
the true laws which govern the movements of the hea- 
venly bodies. Here is indeed a task in which the highest 
powers of the human intellect may be worthily employed. 
Among those who have laboured with the greatest suc- 
cess in the interpretation of the observations made with 
instruments of precision, Le Yerrier holds a highly hon- 
oured place. To him it has been given to provide a 
superb illustration of the success with which the mind 
of man can penetrate the deep things of IN^ature. 

The illustrious Frenchman, Urban Jean Joseph Le Yer- 
rier, was born on the 11th March, 1811, at St. L6, in the 
department of Manche. He received his education in that 
famous school for education in the higher branches of 
science, the Ecole Polytechnique, and acquired there con- 
siderable fame as a mathematician. On leaving the school 
Le Yerrier at first purposed to devote himself to the public 
service, in the department of civil engineering ; and it is 
worthy of note that his earhest scientific work was not in 
those mathematical researches in which he was ultimately 
to become so famous. His duties in the engineering- 
department involved practical chemical research in the 
laboratory. In this he seems to have become very expert, 
and probably fame as a chemist would have been thus 
attained, had not destiny led him into another direction. 
As it was, he did engage in some original chemical re- 
search. His first contributions to science were the fruits 
of his laboratory work ; one of his papers was on the com- 
bination of phosphorus and hydrogen, and another on the 
combination of phosphorus and oxygen. 

His mathematical labours at the Ecole Polytechnique 


had, however, revealed to Le Yerrier that he was endowed 
with the powers requisite for dealing with the subtlest 
instruments of mathematical analysis. When he was 
twenty-eight years old, his first great astronomical inves- 
tigation was brought forth. It will be necessary to enter 
into some explanation as to the nature of this, inasmuch 
as it was the commencement of the life-work which he was 
to pursue. 

If but a single planet revolved around the sun, then 
the orbit of that planet would be an ellipse, and the shape 
and size, as well as the position of the ellipse, would never 
alter. One revolution after another would be traced out, 
exactly in the same manner, in compliance with the force 
continuously exerted by the sun. SujDpose, however, that 
a second planet be introduced into the system. The sun 
will exert its attraction on this second planet also, and it 
will likewise describe an orbit round the central globe. 
We can, however, no longer assert that the orbit in which 
either of the planets moves remains exactly an ellipse. We 
may, indeed, assume that the mass of the sun is enormously 
greater than that of either of the planets. In this case 
the attraction of the sun is a force of such preponderating 
magnitude, that the actual path of each planet remains 
nearly the same as if the other planet were absent. But 
it is impossible for the orbit of each planet not to be 
affected in some degree by the attraction of the other 
planet. The general law of nature asserts that every body 
in space attracts every other body. So long as there is 
only a single planet, it is the single attraction between 
the sun and that planet which is the sole controlling 
principle of the movement, and in consequence of it the 


ellipse is described. But wlien a second planet is intro- 
duced, each of the two bodies is not only subject to the 
attraction of the sun, but each one of the planets attracts 
the other. It is true that this mutual attraction is but 
small, but, nevertheless, it produces some effect. It " dis- 
turbs," as the astronomer says, the elliptic orbit which 
would otherwise have been pursued. Hence it follows 
that in the actual planetary system where there are 
several planets disturbing each other, it is not true to say 
that the orbits are absolutely elliptic. 

At the same time, in any single revolution a planet 
may for most practical purposes be said to be actually 
moving in an ellipse. As, however, time goes on, the 
ellipse gradually varies. It alters its shape, it alters its 
plane, and it alters its position in that plane. If, there- 
fore, we want to study the movements of the planets, 
when great intervals of time are concerned, it is necessary 
to have the means of learning the nature of the move- 
ment of the orbit in consequence of the disturbances it 
has experienced. 

We may illustrate the matter by supposing the planet to 
be running like a railway engine on a track which has been 
laid in a long elliptic path. We may suppose that while 
the planet is coursing along, the shape of the track is gra- 
dually altering. But this alteration may be so slow, that 
it does not appreciably affect the movement of the engine 
in a single revolution. We can also suppose that the plane 
in which the rails have been laid has a slow oscillation in 
level, and that the whole orbit is with more or less uni- 
formity moved slowly about in the plane. 

In short periods of time the changes in the shapes and 


positions of the planetary orbits, in consequence of their 
mutual attractions, are of no great consequence. When, 
however, we bring thousands of years into consideration, 
then the displacements of the planetary orbits attain con- 
siderable dimensions, and have, in fact, produced a pro- 
found effect on the system. 

It is of the utmost interest to investigate the extent to 
which one planet can affect another in virtue of their mu- 
tual attractions. Such investigations demai^d the exercise 
of the highest mathematical gifts. But not alone is intel- 
lectual ability necessary for success in such inquiries. It 
must be united with a patient capacity for calculations of 
an arduous type, protracted, as they frequently have to 
be, through many years of labour. Le Yerrier soon found 
in these profound inquiries adequate scope for the exercise 
of his peculiar gifts. His first important astronomical 
publication contained an investigation of the changes 
which the orbits of several of the planets, including the 
earth, have undergone in times past, and which they will 
undergo in times to come. 

As an illustration of these researches, we may take the 
case of the planet in which we are, of course, especially 
interested, namely, the earth, and we can investigate the 
changes which, in the lapse of time, the earth's orbit 
has undergone, in consequence of the disturbance to which 
it has been subjected by the other planets. In a century, 
or even in a thousand years, there is but little recognisable 
difference in the shape of the track pursued by the earth. 
Yast periods of time are required for the development of the 
large consequences of planetary perturbation. Le Yerrier 
has, however, given us the particulars of what the earth^s 


journey through space has been at intervals of 20,000 
years back from the present date. His furthest calcula- 
tion throws our glance back to the state of the earth's 
track 100,000 years ago, while, with a bound forward, he 
shows us what the earth's orbit is to be in the future, at 
successive intervals of 20,000 years, till a date is reached 
which is 100,000 years in advance of a.d. 1800. 

The talent which these researches displayed brought 
Le Yerrier into notice. At that time the Paris Observa- 
tory was presided over by Arago, a savant who occupies a 
distinguished position in French scientific annals. Arago 
at once perceived that Le Verrier was just the man who 
possessed the qualifications suitable for undertaking a 
problem of great importance and difficulty that had begun 
to force itself on the attention of astronomers. What this 
great problem was, and how astonishing was the solution 
it received, must now be considered. 

Ever since Herschel brought himself into fame by his 
superb discovery of the great planet Uranus, the move- 
ments of this new addition to the solar system were 
scrutinized with care and attention. The jposition of 
Uranus was thus accurately determined from time to time. 
At length, when " sufficient observations of this remote 
planet had been brought together, the route which the 
newly- discovered body pursued through the heavens was 
ascertained by those calculations with which astronomers 
are familiar. It happens, however, that Uranus possesses 
a superficial resemblance to a star. Indeed the resem- 
blance is so often deceptive that long ere its detection as 
a planet by Herschel, it had been observed time after time 
by skilful astronomers, who little thought that the star* 


like point at whicli they looked was anything but a star. 
From these early observations it was possible to determine 
the track of Uranus, and it was found that the great 
planet takes a period of no less than eighty-four years to 
accomplish a circuit. Calculations were made of the 
shape of the orbit in which it revolved before its discovery 
by Herschel, and these were compared with the orbit 
which observations showed the same body to pursue in 
those later years when its planetary character was known. 
It could not, of course, be expected that the orbit should 
remain unaltered ; the fact that the great planets Jupiter 
and Saturn revolve in the vicinity of Uranus must neces- 
sarily imply that the orbit of the latter undergoes con- 
siderable changes. When, however, due allowance has 
been made for whatever influence the attraction of Jupiter 
and Saturn, and we may add of the earth and all the other 
planets, could possibly produce, the movements of Uranus 
were still inexplicable. It was perfectly obvious that 
there must be some other influence at work besides that 
which could be attributed to the planets already known. 

Astronomers could only recognise one solution of such 
a difficulty. It was impossible to doubt that there must 
be some other planet in addition to the bodies at that time 
known, and that the perturbations of Uranus hitherto 
unaccounted for, were due to the disturbances caused by 
the action of this unknown planet. Arago urged Le 
Terrier to undertake the great problem of searching for 
this body, whose theoretical existence seemed demon- 
strated. But the conditions of the search were such that 
it must needs be conducted on principles wholly different 
from any search which had ever before been undertaken 


for a celestial object. For this was not a case in wHcli 
mere survey with a telescope might be expected to lead 
to the discovery. 

Certain facts might be immediately presumed with 
reference to the unknown object. There could be no 
doubt that the unknown disturber of Uranus must be a 
large body with a mass far exceeding that of the earth. 
It was certain, however, that it must be so distant that 
it could only appear from our point of view as a very 
small object. Uranus itself lay beyond the range, or 
almost beyond the range, of unassisted vision. It could 
be shown that the planet by which the disturbance was 
produced revolved in an orbit which must lie outside 
that of Uranus. It seemed thus certain that the planet 
could not be a body visible to the unaided eye. Indeed, 
had it been at all conspicuous its planetary character 
would doubtless have been detected ages ago. The 
unknown body must therefore be a planet which would 
have to be sought for by telescopic aid. 

There is, of course, a profound physical difference be- 
tween a planet and a star, for the star is a luminous sun, 
and the planet is merely a dark body, rendered visible by 
the sunlight which falls upon it. Notwithstanding that 
a star is a sun thousands of times larger than the planet 
and millions of times more remote, yet it is a singular 
fact that telescopic planets possess an illusory resemblance 
to the stars among which their course happens to lie. 
So far as actual appearance goes, there is indeed only one 
criterion by which a planet of this kind can be discri- 
minated from a star. If the planet be large enough the 
telescope will show that it possesses a disc, and has a visible 


and measurable circular outline. This feature a star does 
not exhibit. The stars are indeed so remote that no 
matter how large they may be intrinsically, they only 
exhibit radiant points of light, which the utmost powers 
of the telescope fail to magnify into objects witli an 
appreciable diameter. The older and well-known planets, 
such as Jupiter and Mars, possess discs, which, though, not 
visible to the unaided eye, were clearly enough discernible 
with the slightest telescopic power. But a very remote 
planet like Uranus, though it possessed a disc large 
enough to be quickly appreciated by the consummate ob- 
serving skill of Herschel, was nevertheless so stellar in 
its appearance, that it had been observed no fewer than 
seventeen times by experienced astronomers prior to 
Herschel. In each case the planetary nature of the 
object had been overlooked, and it had been taken for 
granted that it was a star. It presented no difference 
which was sufficient to arrest attention. 

As the unknown body by which Uranus was disturbed 
was certainly much more remote than Uranus, it seemed 
to be certain that though it might show a disc percep- 
tible to very close inspection, yet that the disc must be 
so minute as not to be detected except with extreme care. 
In other words, it seemed probable that the body which 
was to be sought for could not readily be discriminated 
from a small star, to which class of object it bore a super- 
ficial resemblance, though, as a matter of fact, there was 
the profoundest difference between the two bodies. 

There are on the heavens many hundreds of thousands 
of stars, and the problem of identifying the planet, if 
indeed it should lie among these stars, seemed a very 


complex matter. Of course it is tlie abundant presence 
of the stars which, causes the difficulty. If the stars 
could have been got rid of, a sweep over the heavens 
would at once disclose all the planets which are bright 
enough to be visible with the telescopic power employed. 
It is the fortuitous resemblance of the planet to the stars 
which enables it to escape detection. To discriminate 
the planet among stars everywhere in the sky would be 
almost impossible. If, however, some method could be 
devised for localizing that precise region in which the 
planet's existence might be presumed, then the search 
could be undertaken with some prospect of success. 

To a certain extent the problem of localizing the region 
on the sky in which the planet might be expected 
admitted of an immediate limitation. It is known that 
all the planets, or perhaps I ought rather to say, all the 
great planets, confine their movements to a certain zone 
around the heavens. This zone extends some way on 
either side of that line called the ecliptic in which the 
earth pursues its journey around the sun. It was there- 
fore to be inferred that the new planet need not be 
sought for outside this zone. It is obvious that this con- 
sideration at once reduces the area to be scrutinized to a 
small fraction of the entire heavens. But even within 
the zone thus defined there are many thousands of stars. 
It would seem a hopeless task to detect the new planet 
unless some further limitation to its position could be 

It was accordingly suggested to Le Verrier that he 
should endeavour to discover in what particular part of 
the strip of the celestial sphere which we have indicated 


the search for the unknown planet should be instituted. 
The materials available to the mathematician for the 
solution of this problem were to be derived solely from 
the discrepancies between the calculated places in which 
Uranus should be found, taking into account the known 
causes of disturbance, and the actual places in which 
observation had shown the planet to exist. Here was 
indeed an unprecedented problem, and one of extra- 
ordinary difficulty. Le Yerrier, however, faced it, and, to 
the astonishment of the world, succeeded in carrying it 
through to a brilliant solution. We cannot here attempt 
to enter into any account of the mathematical investiga- 
tions that were necessary. All that we can do is to give 
a general indication of the method which had to be 

Let us suppose that a planet is revolving outside 
Uranus, at a distance which is suggested by the several 
distances at which the other planets are dispersed around 
the sun. Let us assume that this outer planet has 
started on its course, in a prescribed path, and that it has 
a certain mass. It will, of course, disturb the motion of 
Uranus, and in consequence of that disturbance Uranus 
will follow a path the nature of which can be determined 
by calculation. It will, however, generally be found that 
the path so ascertained does not tally with the actual path 
which observations have indicated for Uranus. This 
demonstrates that the assumed circumstances of the un- 
known planet must be in some respects erroneous, and 
the astronomer commences afresh with an amended orbit. 
At last after many trials, Le Yerrier ascertained that, 
by assuming a certain size, shape, and position for the un- 


known planet's orbit, and a certain value for the mass of 
the hypothetical body, it would be possible to account for 
the observed disturbances of Uranus. Gradually it became 
clear to the perception of this consummate mathematician, 
not only that the difficulties in the movements of TJranus 
could be thus explained, but that no other explanation 
need be sought for. It accordingly appeared that a planet 
possessing the mass which he had assigned, and moving in 
the orbit which his calculations had indicated, must 
indeed exist, though no eye had ever beheld any such 
body. Here was, indeed, an astonishing result. The 
mathematician sitting at his desk, by studying the 
observations which had been supplied to him of one planet, 
is able to discover the existence of another planet, and even 
to assign the very position which it must occupy, ere ever 
the telescope is invoked for its discovery. 

Thus it was that the calculations of Le Yerrier narrowed 
greatly the area to be scrutinised in the telescopic search 
which was presently to be instituted. It was already 
known, as we have just pointed out, that the planet must 
lie somewhere on the ecliptic. The French mathematician 
had now further indicated the spot on the ecliptic at 
which, according to his calculations, the planet must 
actually be found. And now for an episode in this 
history which will be celebrated so long as science shall 
endure. It is nothing less than the telescopic confirmation 
of the existence of this new planet, which had previously 
been indicated only by mathematical calculation. Le 
Yerrier had not himself the Instruments necessary for 
studying the heavens, nor did he possess the skill of 
the practical astronomer. He, therefore, wrote to Dr. 


Galle, of the Observatory at Berlin, requesting him to 
undertake a telescopic search for the new planet in the 
vicinity which the mathematical calculation had indicated 
for the whereabouts of the planet at that particular time. 
Le Verrier added that he thought the planet ought to 
admit of being recognised by the possession of a disc 
sufficiently definite to mark the distinction between it 
and the surrounding stars. 

It was the 23rd September, 1846, when the request 
from Le Yerrier reached the Berlin Observatory, and the 
night was clear, so that the memorable search was made 
on the same evening. The investigation was facilitated 
by the circumstance that a diligent observer had recently 
compiled elaborate star maps for certain tracts of the 
heavens lying in a sufficiently wide zone on both sides of 
the equator. These maps were as yet only partially com- 
plete, but it happened that Hora. XXI., which included 
the very spot which Le Terrier's results referred to, had 
been just issued. Dr. Galle had thus before his eyes a 
chart of all the stars which were visible in that part of 
the heavens at the time when the map was made. The 
advantage of such an assistance to the search could 
hardly be over-estimated. It at once gave the astronomer 
another method of recognising the planet besides that 
afforded by its possible possession of a disc. For as the 
planet was a moving body, it would not have been in the 
same place relatively to the stars at the time when the 
map was constructed, as it occupied some years later when 
the search was being made. If the body should be 
situated in the spot which Le Terrier's calculations indi- 
cated in the autumn of 1 846, then it might be regarded 


as certain that it would not be found in tliat same place on 
a map drawn some years previously. 

The search to be undertaken consisted in a comparison 
made point by point between the bodies shown on the map, 
and those stars in the sky which Dr. Galle's telescope 
revealed. In the course of this comparison it pre- 
sently appeared that a star-like object of the eighth 
magnitude, which was quite a conspicuous body in the 
telescope, was not represented in the map. This at once 
attracted the earnest attention of the astronomer, and 
raised his hopes that here was indeed the planet. !N^or 
were these hopes destined to be disappointed. It could 
not be supposed that a star of the eighth magnitude would 
have been overlooked in the preparation of a chart whereon 
stars of many lower degrees of brightness were set down. 
One other supposition was, of course, conceivable. It 
might have been that this suspicious object belonged to 
the class of variables, for there are many such stars whose 
brightness fluctuates, and if it had happened that the map 
was constructed at a time when the star in question had 
but feeble brilliance, it might have escaped notice. It is 
also well known that sometimes new stars suddenly 
develop, so that the possibility that what Dr. Galle saw 
should have been a variable star or should have been a 
totally new star had to be provided against. 

Fortunately a test was immediately available to decide 
whether the new object was indeed the long sought for 
planet, or whether it was a star of one of the two classes to 
which I have just referred. A star remains fixed, but a 
planet is in motion. No doubt when a planet lies at the 
distance at which this new planet was believed to be 


situated, its apparent motion would be so slow that it 
would not be easy to detect any change in the course of a 
single night's observation. Dr. Galle, however, addressed 
himself with much skill to the examination of the place 
of the new body. Even in the course of the night he 
thought he detected slight movements, and he awaited 
with much anxiety the renewal of his observations on the 
subsequent evenings. His suspicions as to the movement 
of the body were then amply confirmed, and the planetary 
nature of the new object was thus unmistakably detected. 
Great indeed was the admiration of the scientific world 
at this superb triumph. Here was a mighty planet whose 
very existence was revealed by the indications afforded 
by refined mathematical calculation. At once the name 
of Le Yerrier, already known to those conversant with 
the more profound branches of astronomy, became every- 
where celebrated. It soon, however, appeared, that the 
fame belonging to this great achievement had to be shared 
between Le Yerrier and another astronomer, J. C. Adams, 
of Cambridge. In our chapter on this great English 
mathematician we shall describe the manner in which he 
was independently led to the same discovery. 

Directly the planetary nature of the newly-discovered 
body had been established, the great observatories naturally 
included this additional member of the solar system in 
their working lists, so that day after day its place was 
carefully determined. When sufficient time had elapsed 
the shape and position of the orbit of the body became 
known. Of course, it need hardly be said that observations 
applied to the planet itself must necessarily provide a far 
more accurate method of determining the path which it 


follows, than would be possible to Le Yerrier, wben all lie 
bad to base bis calculations upon was the influence of the 
planet reflected, so to speak, from Uranus. It may be 
noted that tbe true elements of tbe planet, wben revealed 
by direct observation, showed that there was a consider- 
able discrepancy between the track of the planet which 
Le Yerrier had announced, and that which the planet was 
actually found to pursue. 

The name of the newly- discovered body had next to be 
considered. As the older members of the system were 
already known by the same names as great heathen 
divinities, it was obvious that some similar source should 
be invoked for a suggestion as to a name for the most 
recent planet. The fact that this body was so remote in 
the depths of space, not unnaturally suggested the name 
" Neptune." Such is accordingly the accepted designation 
of that mighty globe which revolves in the track that 
at present seems to trace out the frontiers of our system. 

Le Yerrier attained so much fame by this discovery, 
that when, in 1854, Arago's place had to be filled at the 
head of the great Paris Observatory, it was universally felt, 
that the discoverer of Neptune was the suitable man to 
assume the office which corresponds in France to that of 
the Astronomer Boyal in England. It was true that the 
work of the astronomical mathematician had hitherto been 
of an abstract character. His discoveries had been made 
at his desk and not in the observatory, and he had no 
practical acquaintance with the use of astronomical instru- 
ments. However, he threw himself into the technical 
duties of the observatory with vigour and determination. 
He endeavoured to inspire the officers of the establishment 
with enthusiasm for that systematic work which is so 



necessary for tlie accomplishment of useful astronomical 
research. It must, however, be admitted that Le Yerrier 
was not gifted with those natural qualities which would 
make him adapted for the successful administration of such 
an establishment. Unfortunately disputes arose between 
the Director and his staff. At last the difficulties of the 
situation became so great that the only possible solution 
was to supersede Le Yerrier, and he was accordingly 
obliged to retire. He was succeeded in his high office by 
another eminent mathematician, M. Delaunay, only less 
distinguished than Le Yerrier himself. 

Eelieved of his official duties, Le Yerrier returned to 
the mathematics he loved. In his non-official capacity 
he continued to work with the greatest ardour at his 
researches on the movements of the planets. After the 
death of M. Delaunay, who was accidentally drowned in 
1873, Le Yerrier was restored to the directorship of the 
observatory, and he continued to hold the office until his 

The nature of the researches to which the life of Le 
Yerrier was subsequently devoted are not such as admit 
of description in a general sketch like this, where the 
language, and still less the symbols, of mathematics could 
not be suitably introduced. It may, however, be said in 
general that he was particularly engaged with the study of 
the effects produced on the movements of the planets by 
their mutual attractions. The importance of this work 
to astronomy consists, to a considerable extent, in the fact 
that by such calculations we are enabled to prepare tables 
by which the places of the different heavenly bodies can 
be predicted for our almanacs. To this task Le Yerrier 
devoted himself, and the amount of work he has accom- 


plished would perhaps have been deemed impossible bad 
it not been actually done. 

The superb success which had attended Le Yerrier's 
efforts to explain the cause of the perturbations of Uranus, 
naturally led this wonderful computer to look for a simi- 
lar explanation of certain other irregularities in planetary 
movements. To a large extent he succeeded in showing 
how the movements of each of the great planets could be 
satisfactorily accounted for by the influence of the attrac- 
tions of the other bodies of the same class. One circum- 
stance in connection with these investigations is suffi- 
ciently noteworthy to require a few words here. Just as 
at the opening of his career, Le Yerrier had discovered 
that Uranus, the outermost planet of the then known 
system, exhibited the influence of an unknown external 
body,- so now it appeared to him that Mercury, the inner- 
most body of our system, was also subjected to some dis- 
turbances, which could not be satisfactorily accounted for 
as consequences of any known agents of attraction. The 
ellipse in which Mercury revolved was animated by a 
slow movement, which caused it to revolve in its plane. 
It appeared to Le Yerrier that this displacement was 
incapable of explanation by the action of any of the 
known bodies of our system. He was, therefore, induced 
to try whether he could not determine from the dis- 
turbances of Mercury the existence of some other planet, 
at present unknown, which revolved inside the orbit of 
the known planet. Theory seemed to indicate that the 
observed alteration in the track of the planet could be 
thus accounted for. He naturally desired to obtain tele- 
scopic confirmation which might verify the existence of 
such a body in the same way as Dr. (jalle verified the 


existence of IN'eptune. If there were, indeed, an intra- 
mercurial planet, then it must occasionally cross between 
the earth and the sun, and might now and then be 
expected to be witnessed in the actual act of transit. So 
confident did Le Yerrier feel in the existence of such a 
body that an observation of a dark object in transit, by 
Lescarbault on 26th March, 1859, was believed by the 
mathematician to be the object which his theory indicated. 
Le Verrier also thought it likely that another transit of 
the same object would be seen in March, 1877. N"othing 
of the kind was, however, witnessed, notwithstanding that 
an assiduous watch was kept, and the explanation of the 
change in Mercury's orbit must, therefore, be regarded as 
still to be sought for. 

Le Terrier naturally received every honour that could 
be bestowed upon a man of science. The latter part of 
his life was passed during the most troubled period of 
modern French history. He was a supporter of the 
Imperial Dynasty, and during the Commune he expe- 
rienced much anxiety; indeed, at one time grave fears 
were entertained for his personal safety. 

Early in 1877 his health, which had been gradually 
failing for some j^ears, began to give way. He appeared 
to rally somewhat in the summer, but in September he 
sank rapidly, and died on Sunday, the 28rd of that month. 
His remains were borne to the cemetery on Mont 
Parnasse in a public funeral. Among his pall-bearers 
were leading men of science, from other countries as well 
as France, and the memorial discourses pronounced at the 
grave expressed their admiration of his talents and of the 
greatness of the services he had rendered to science. 

A A 


The illustrious matliematician who, among Englislimen, 
at all events, was second only to Newton by his discoveries 
in theoretical astronomy, was born on June the 5th, 1819, 
at the farmhouse of Lidcot, seven miles from Launceston, 
in Cornwall. His early education was imparted under 
the guidance of the E-ev. John Couch Grylls, a first cousin 
of his mother. He appears to have received an education 
of the ordinary school type in classics and mathematics, 
but his leisure hours were largely devoted to studying 
what astronomical books he could find in the library of 
the Mechanics' Institute at Devonport. He was twenty 
years old when he entered St. John's College, Cambridge. 
His career in the University was one of almost unparal- 
leled distinction, and it is recorded that his answering at 
the Wranglership examination, where he came out at the 
head of the list in 1843, was so high that he received 
more than double the marks awarded to the Second 

Among the papers found after his death was the fol- 
lowing memorandum, dated July the 3rd, 1841 : " Formed 
a design at the beginning of this week of investigating, 
as soon as possible after taking my degree, the irregu- 

ADAMS. 355 

laritles in the motion of Uranus, wliich. are as yet 
unaccounted for, in order to find whether they may be 
attributed to the action of an undiscovered planet beyond 
it ; and, if possible, thence to determine the elements of 
its orbit approximately, which would lead probably to its 

After he had taken his degree, and had thus obtained 
a little relaxation from the lines within which his studies 
had previously been necessarily confined, Adams devoted 
himself to the study of the perturbations of Uranus, in 
accordance with the resolve which we have just seen that 
he formed while he was still an undergraduate. As a 
first attempt he made the supposition that there might be 
a planet exterior to Uranus, at a distance which w^as 
double that of Uranus from the sun. Having completed 
his calculation as to the effect which such a hypothetical 
planet might exercise upon the movement of Uranus, he 
came to the conclusion that it would be quite possible to 
account completely for the unexplained difficulties by the 
action of an exterior planet, if only that planet were of 
adequate size and had its orbit properly placed. It was 
necessary, however, to follow up the problem more pre- 
cisely, and accordingly an application was made through 
Professor Challis, the Director of the Cambridge Observa- 
tory, to the Astronomer E-oyal, with the object of obtain- 
ing from the observation^- made at Greenwich Observatory 
more accurate values for the disturbances suffered by 
Uranus. Basing his work on the more precise materials 
thus available, Adams undertook his calculations anew, 
and at last, with his completed results, he called at Green- 
wich Observatory on October the 21st, 1845. He there 


left for tlie Astronomer Eoyal a paper whicli contained 
tlie results at whicli lie had arrived for the mass and the 
mean distance of the hypothetical planet as well as the 
other elements necessary for calculating its exact position. 
As we have seen in the preceding chapter, Le Verrier 
had been also investigating the same problem. The place 
which Le Yerrier assigned to the hypothetical disturbing 
planet for the beginning of the year 1847, was within a 
degree of that to which Adams's computations pointed, 
and which he had communicated to the Astronomer Royal 
seven months before Le Yerrier' s work appeared. On 
July the 29th, 1846, Professor Challis commenced to search 
for the unknown object with the Northumberland telescope 
belonging to the Cambridge Observatory. He confined 
his attention to a limited region in the heavens, extending 
around that point to which Mr. Adams' calculations 
pointed. The relative places of all the stars, or rather 
star-like objects within this area, were to be carefully 
measured. When the same observations were repeated a 
week or two later, then the distances of the several pairs 
of stars from each other would be found unaltered, but 
any planet which happened to lie among the objects 
measured would disclose its existence by the alterations in 
distance due to its motion in the interval. This method 
of search, though no doubt it must ultimately have proved 
successful, was necessarily a very tedious one, but to Pro- 
fessor Challis, unf ortunatel}/ ., no other method was avail- 
able. Thus it happened that, though Challis commenced 
his search at Cambridge two months earlier than Galle at 
Berlin, yet, as we have already explained, the possession 
of accurate star-maps by Dr. Galle enabled him to dis- 



John Couch Adams. 

cover the planet on the very first night that he looked 
for it. 

The rival claims of Adams and Le Yerrier to the dis- 
covery of JSTeptune, or rather, we should say, the claims 
put forward by their respective champions, for neither of 
the illustrious investigators themselves condescended to 
enter into the personal aspect of the question, need not 


be further discussed here. The main points of the con- 
troversy have been long since settled, and we cannot de 
better than quote the words of Sir John Herschel when 
he addressed the Royal Astronomical Society in 1848 : — 

" As genius and destiny have joined the names of Le 
Verrier and Adams, I shall by no means put them 
asunder ; nor will they ever be pronounced apart so long 
as language shall celebrate the triumphs of science in her 
sublimest walks. On the great discovery of Neptune, 
which may be said to have surpassed, by intelligible and 
legitimate means, the wildest pretensions of clairvoyance, 
it would now be quite superfluous for me to dilate. That 
glorious event and the steps which led to it, and the 
various lights in which it has been placed, are already 
familiar to every one having the least tincture of science. 
I will only add that as there is not, nor henceforth ever 
can be, the slightest rivalry on the subject between these 
two illustrious men — as they have met as brothers, and 
as such will, I trust, ever regard each other — we have 
made, we could make, no distinction between them on 
this occasion. May they both long adorn and augment 
our science, and add to their own fame, already so high 
and pure, by fresh achievements." 

Adams was elected a Fellow of St. John's College, 
Cambridge, in 1843 ; but as he did not take holy orders, 
his Fellowship, in accordance with the rules then exist- 
ing, came to an end in 1852. In the following year he 
was, however, elected to a Fellowship at Pembroke 
College, which he retained until the end of his life. In 
1858 he was appointed Professor of Mathematics in the 
University of St. Andrews, but his residence in the 

ADAMS. 359 

north was only a brief one, for in tlie same year lie was 
recalled to Cambridge as Lowndean Professor of Astro- 
nomy and Geometry, in succession to Peacock. In 1861 
Challis retired from tbe Directorship of the Cambridge 
Observatory, and Adams was appointed to succeed him. 

The discovery of Neptune was a brilliant inauguration 
of the astronomical career of Adams. He worked at, 
and wrote upon, the theory of the motions of Biela's 
comet; he made important corrections to the theory 
of Saturn; he investigated the mass of Uranus, a 
subject in which he was naturally interested from its 
importance in the theory of Neptune ; he also improved the 
methods of computing the orbits of double stars. But all 
these must be regarded as his minor labours, for next to 
the discovery of Neptune the fame of Adams mainly 
rests on his researches upon certain movements of the 
moon, and upon the November meteors. 

The periodic time of the moon is the interval required 
for one circuit of its orbit. This interval is known 
with accuracy at the present day, and by means of 
the ancient eclipses the period of the moon's revolu- 
tion two thousand years ago can be also ascertained. It 
had been discovered by Halley that the period which the 
moon requires to accomplish each of its revolutions around 
the earth has been steadily, though no doubt slowly, 
diminishing. The change thus produced is not appre- 
ciable when only small intervals of time are considered, 
but it becomes appreciable when we have to deal with 
intervals of thousands of years. The actual effect which 
is produced by the lunar acceleration, for so this pheno- 
menon is called, may be thus estimated. If we suppose 


that the moon had, throughout the ages, revolved around 
the earth in precisely the same periodic time which it has 
at present, and if from this assumption we calculate back 
to find where the moon must have been about two thou- 
sand years ago, we obtain a position which the ancient 
eclipses show to be different from that in which the 
moon was actually situated. The interval between the 
position in which the moon would have been found two 
thousand years ago if there had been no acceleration, and 
the position in which the moon was actually placed, 
amounts to about a degree, that is to say, to an arc on the 
heavens which is twice the moon's apparent diameter. 

If no other bodies save the earth and the moon were 
present in the universe, it seems certain that the motion 
of the moon would never have exhibited this acceleration. 
In such a simple case as that which I have supposed the 
orbit of the moon would have remained for ever absolutely 
unchanged. It is, however, well known that the presence 
of the sun exerts a disturbing influence upon the move- 
ments of the moon. In each revolution our satellite is 
continually drawn aside by the action of the sun from the 
place which it would otherwise have occupied. These 
irregularities are known as the perturbations of the lunar 
orbit, they have long been studied, and the majority of 
them have been satisfactorily accounted for. It seems, 
however, to those who first investigated the question that 
the phenomenon of the lunar acceleration could not be 
explained as a consequence of solar perturbation, and, as 
no other agent competent to produce such effects was 
recognised by astronomers, the lunar acceleration pre- 
sented an unsolved enigma. 

ADAMS, 361 

At the end of the last century the illustrious French 
mathematician Laplace undertook a new investigation of 
the famous problem, and was rewarded with a success 
which for a long time appeared to be quite complete. 
Let us suppose that the moon lies directly between the 
earth and the sun, then both earth and moon are pulled 
towards the sun by the solar attraction ; as, however, the 
moon is the nearer of the two bodies to the attracting 
centre it is pulled the more energetically, and conse- 
quently there is an increase in the distance between the 
earth and the moon. Similarly when the moon happens 
to lie on the other side of the earth, so that the earth is 
interposed directly between the moon and the sun, the 
solar attraction exerted upon the earth is more powerful 
than the same influence upon the moon. Consequently 
in this case, also, the distance of the moon from the earth 
is increased by the solar disturbance. These instances 
will illustrate the general truth, that, as one of the conse- 
quences of the disturbing influence exerted by the sun 
upon the earth-moon system, there is an increase in the 
dimensions of the average orbit which the moon describes 
around the earth. As the time required by the moon to 
accomplish a journey round the earth depends upon its 
distance from the earth, it follows that among the influ- 
ences of the sun upon the moon there must be an enlarge- 
ment of the periodic time, from what it would have been 
had there been no solar disturbing action. 

This was known long before the time of Laplace, but it 
did not directly convey any explanation of the lunar ac- 
celeration. It no doubt amounted to the assertion that the 
moon's periodic time was slightly augmented by the dis- 


turbance, but it did. not give any grounds for suspecting 
tbat there was a continuous cbange in progress. It was, 
however, apparent that the periodic time was connected 
with, the solar disturbance, so that, if there were any altera- 
tion in the amount of the sun's disturbing effect, there 
must be a corresponding alteration in the moon's periodic 
time. Laplace, therefore, perceived that, if he could dis- 
cover any continuous change in the ability of the sun for 
disturbing the moon, he would then have accounted for a 
continuous change in the moon's periodic time, and that 
thus an explanation of the long- vexed question of the 
lunar acceleration might be forthcoming. 

The capability of the sun for disturbing the earth-moon 
system is obviously connected with the distance of the earth 
from the sun. If the earth moved in an orbit which 
underwent no change whatever, then the efficiency of the 
sun as a disturbing agent would not undergo any change 
of the kind which was sought for. But if there were any 
alteration in the shape or size of the earth's orbit, then that 
might involve such changes in the distance between the 
earth and the sun as would possibly afford the desired agent 
for producing the observed lunar effect. It is known that 
the earth revolves in an orbit which, though nearly 
circular, is strictly an ellipse. If the earth were the 
only planet revolving around the sun then that ellipse 
would remain unaltered from age to age. The earth is, 
however, only one of a large number of planets which 
circulate around the great luminary, and are guided and 
controlled by his supreme attracting power. These planets 
mutually attract each other, and in consequence of their 
mutual attractions, the orbits of the planets are disturbed 

ADAMS. 363 

from tlie simple elliptic form which they would otherwise 
possess. The movement of the earth, for instance, is not, 
strictly speaking, performed in an elliptical orbit. We 
may, however, regard it as revolving in an ellipse pro- 
vided we admit that the ellipse is itself in slow motion. 

It is a remarkable characteristic of the disturbing effects 
of the planets that the ellipse in which the earth is at 
any moment moving always retains the same length ; 
that is to say, its longest diameter is invariable. In all 
other respects the ellipse is continually changing. It 
alters its position, it changes its plane, and, most impor- 
tant of all, it changes its eccentricity. Thus, from age to 
age the shape of the track which the earth describes may 
at one time be growing more nearly a circle, or at another 
time may be departing more widely from a circle. These 
alterations are very small in amount, and they take place 
with extreme slowness, but they are in incessant progress, 
and their amount admits of being accurately calculated. 
At the present time, and for thousands of years past, as well 
as for thousands of years to come, the eccentricity of the 
earth's orbit is diminishing, and consequently the orbit 
described by the earth each year is becoming more nearly 
circular. We must, however, remember that under all 
circumstances the length of the longest axis of the ellipse 
is unaltered, and consequently the size of the track which 
the earth describes around the sun is gradually increas- 
ing. In other words, it may be said that during the 
present ages the average distance between the earth and 
the sun is waxing greater in consequence of the pertur- 
bations which the earth experiences from the attraction 
of the other planets. We have, however, already seen that 


the efficiency of the solar attraction for disturbing the 
moon's movement depends on the distance between the 
earth and the sun. As therefore the average distance 
between the earth and the sun is increasing, at all events 
during the thousands of years over which our observations 
extend, it follows that the ability of the sun for disturb- 
ing the moon must be gradually diminishing. 

It has been pointed out that, in consequence of the 
solar disturbance, the orbit of the moon must be some- 
what enlarged. As it now appears that the solar disturb- 
ance is on the whole declining, it follows that the orbit 
of the moon, which has to be adjusted relatively to the 
average value of the solar disturbance, must also be 
gradually declining. In other words, the moon must be 
approaching nearer to the earth in consequence of the 
alterations in the eccentricity of the earth's orbit pro- 
duced by the attraction of the other planets. It is true 
that the change in the moon's position thus arising is an 
extremely small one, and the consequent effect in accelerat- 
ing the moon's motion is but very slight. It is in fact 
almost imperceptible, except when great periods of time 
are involved. Laplace undertook a calculation on this 
subject. He knew what the efficiency of the planets in 
altering the dimensions of the earth's orbit amounted to ; 
from this he was able to determine the changes that 
would be propagated into the motion of the moon. Thus 
he ascertained, or at all events thought he had ascertained, 
that the acceleration of the moon's motion, as it had been 
inferred from the observations of the ancient eclipses 
which have been handed down to us, could be completely 
accounted for as a consequence of planetary perturbation. 





I ^ ^ 



This was regarded as a great scientific triumph. Our 
belief in the universality of the law of gravitation would, 
in fact, have been seriously challenged unless some expla- 
nation of the lunar acceleration had been forthcoming. 

For about fifty years no one questioned the truth 
of Laplace's investigation. When a mathematician of his 
eminence had rendered an explanation of the remarkable 
facts of observation which seemed so complete, it is not 
surprising that there should have been but little temptation 
to doubt it. On undertaking a new calculation of the same 
question, Professor Adams found that Laplace had not 
pursued this approximation sufficiently far, and that con- 
sequently there was a considerable error in the result of 
his analysis. Adams, it must be observed, did not impugn 
the value of the lunar acceleration which Halley had 
deduced from the observations, but what he did show was, 
that the calculation by which Laplace thought he had pro- 
vided an explanation of this acceleration was erroneous. 
Adams, in fact, proved that the planetary influence which 
Laplace had detected only possessed about half the 
efficiency which the great French mathematician had 
attributed to it. There were not wanting illustrious ma- 
thematicians who came forward to defend the calculations 
of Laplace. They computed the question anew and 
arrived at results practically coincident with those he had 
given. On the other hand certain distinguished ma- 
thematicians at home and abroad verified the results of 
Adams. The issue was merely a mathematical one. It 
had only one correct solution. Gradually it appeared 
that those who opposed Adams presented a number of 
different solutions, all of them discordant with his, and, 

ADAMS. 367 

usually, discordant with each, other. Adams showed dis- 
tinctly where each of these investigators had fallen into 
error, and at last it became universally admitted that the 
Cambridge Professor had corrected Laplace in a very 
fundamental point of astronomical theory. 

Though it was desirable to have learned the truth, yet the 
breach between observation and calculation which Laplace 
was believed to have closed thus became reopened. La- 
place's investigation, had it been correct, would have 
exactly explained the observed facts. It was, however, 
now shown that his solution was not correct, and that the 
lunar acceleration, when strictly calculated as a consequence 
of solar perturbations, only produced about half the effect 
which was wanted to explain the ancient eclipses com- 
pletely. It now seems certain that there is no means of 
accounting for the lunar acceleration as a direct conse- 
quence of the laws of gravitation, if we suppose, as we have 
been in the habit of supposing, that the members of the 
solar system concerned may be regarded as rigid particles. 
It has, however, been suggested that another explanation 
of a very interesting kind may be forthcoming, and this 
we must endeavour to set forth. 

It will be remembered that we have to explain why the 
period of revolution of the moon is now shorter than it 
used to be. If we imagine the length of the period to be 
expressed in terms of days and fractions of a day, that 
is to say, in terms of the rotations of the earth around its 
axis, then the difficulty encountered is, that the moon now 
requires for each of its revolutions around the earth rather 
a smaller number of rotations of the earth around its axis 
than used formerly to be the case. Of course this may be 


explained by tlie fact that the moon is now moving more 
swiftly than of yore, but it is obvious that an explanation 
of quite a different kind might be conceivable. The moon 
may be moving just at the same pace as ever, but the 
length of the day may be increasing. If the length of 
the day is increasing, then, of course, a smaller number of 
days will be required for the moon to perform each revo- 
lution, even though the moon's period was itself really 
unchanged. It would, therefore, seem as if the phe- 
nomenon known as the lunar acceleration is the result of 
the two causes. The first of these is that discovered by 
Laplace, though its value was overestimated by him, in 
which the perturbations of the earth by the planets in- 
directly affect the motion of the moon. The remaining 
part of the acceleration of our satellite is apparent rather 
than real, it is not that the moon is moving more quickly, 
but that our time-piece, the earth, is revolving more 
slowly, and is thus actually losing time. It is interesting 
to note that we can detect a physical explanation for the 
apparent checking of the earth's motion which is thus 
manifested. The tides which ebb and flow on the earth 
exert a brake-like action on the revolving globe, and there 
can be no doubt that they are gradually reducing its 
speed, and thus lengthening the day. It has accordingly 
been suggested that it is this action of the tides which 
produces the supplementary effect necessary to com- 
plete the physical explanation of the lunar acceleration, 
though it would perhaps be a little premature to assert 
that this has been fully demonstrated. 

The third of Professor Adams' most notable achieve- 
ments was connected with the great shower of November 

ADAMS. 369 

meteors which astonished the world in 1866. This 
splendid display concentrated the attention of astronomers 
on the theory of the movements of the little objects by 
which the display was produced. For the definite dis- 
covery of the track in which these bodies revolve, we 
are indebted to the labours of Professor Adams, who, by 
a brilliant piece of mathematical work, completed the 
edifice whose foundations had been laid by Professor 
Newton, of Yale, and other astronomers. 

Meteors revolve around the sun in a vast swarm, every 
individual member of which pursues an orbit in accord* 
ance with the well-known laws of Kepler. In order to 
understand the movements of these objects, to account 
satisfactorily for their periodic recurrence, and to predict 
the times of their appearance, it became necessary to learn 
the size and the shape of the track which the swarm 
followed, as well as the position which it occupied. 
Certain features of the track could no doubt be readily 
assigned. The fact that the shower recurs on one par- 
ticular day of the year, viz., JSTovember 13th, defines one 
point through which the orbit must pass. Th? position 
on the heavens of the radiant point from which the 
meteors appear to diverge, gives another element in 
the track. The sun must of course be situated at the 
focus, so that only one further piece of information, 
namely, the periodic time, will be necessary to complete 
our knowledge of the movements of the system. Pro- 
fessor H. Newton, of Yale, had shown that the choice of 
possible orbits for the meteoric swarm is limited to five. 
There is, first, the great ellipse in which we now know the 
meteors revolve once every 33i years. There is next an 

B B 


orbit of a nearly circular kind in wliicli tlie periodic time 
would be a little more tban a year. There is a similar 
track in wbicb tbe periodic time would be a few days 
short of a year, while two other smaller orbits would also 
be conceivable. Professor I^ewton had pointed out a 
test by which it would be possible to select the true 
orbit, which we know must be one or other of these five. 
The mathematical difficulties which attended the applica- 
tion of this test were no doubt great, but they did not 
baffle Professor Adams. 

There is a continuous advance in the date of this meteoric 
shower. The meteors now cross our track at the point 
occupied by the earth on JN'ovember 13th, but this point 
is gradually altering. The only influence known to us 
which could account for the continuous change in the 
plane of the meteor's orbit arises from the attraction of 
the various planets. The problem to be solved may 
therefore be attacked in this manner. A specified amount 
of change in the plane of the orbit of the meteors is known 
to arise, and the changes which ought to result from the 
attraction of the planets can bQ computed for each of the 
five possible orbits, in one of which it is certain that the 
meteors must revolve. Professor Adams undertook the 
work. Its difficulty [principally arises from the high 
eccentricity of the largest of the orbits, which renders 
the more ordinary methods of calculation inapplicable. 
After some months of arduous labour the work was com- 
pleted, and in April, 1867, Adams announced his solu- 
tion of the problem. He showed that if the meteors 
revolved in the largest of the five orbits, with the 
periodic time of 33 i years, the perturbations of Jupiter 

ADAMS. 371 

would account for a change to the extent of twenty 
minutes of arc in the point in which the orbit crosses the 
earth's track. The attraction of Saturn would augment 
this by seven minutes, and TJranus would add one minute 
more, while the influence of the Earth and of the other 
planets would be inappreciable. The accumulated effect 
is thus twenty- eight minutes, which is practically coinci- 
dent with the observed value as determined by Professor 
Newton from an examination of all the showers of which 
there is any historical record. Having thus showed that 
the great orbit was a possible path for the meteors, 
Adams next proved that no one of the other four orbits 
would be disturbed in the same manner. Indeed, it 
appeared that not half the observed amount of change 
could arise in any orbit except in that one with the long 
period. Thus was brought to completion the interesting 
research which demonstrated the true relation of the 
meteor swarm to the solar system. 

Besides those memorable scientific labours with which 
his attention was so largely engaged. Professor Adams 
found time for much other study. He occasionally allowed 
himself to undertake as a relaxation some pieces of numeri- 
cal calculation, so tremendously long that we can only look 
on them with astonishment. He has calculated certain 
important mathematical constants accurately to more than 
two hundred places of decimals.' He was a diligent 
reader of works on history, geology, and botany, and 
his arduous labours were often beguiled by novels, of 
which, like many other great men, he was very fond. 
He had also the taste of a collector, and he brought 
together about eight hundred volumes of early printed 


works, many of considerable rarity and value. As to his 
personal character, I may quote the words of Dr. Glaisher 
when he says, " Strangers who first met him were in- 
variably struck by his simple and unafi'ected manner. 
He was a delightful companion, always cheerful and 
genial, showing in society but few traces of his really 
shy and retiring disposition. His nature was sympa- 
thetic and generous, and in few men have the moral and 
intellectual qualities been more perfectly balanced." 

In 1863 he married the daughter of Haliday Bruce, Esq., 
of Dublin, and up to the close of his life he lived at the 
Cambridge Observatory, pursuing his mathematical work 
and enjoying the society of his friends. 

He died, after a long illness, on 21st January, 1892, 
and was interred in St. Giles's Cemetery, on the Hunt- 
ingdon Road, Cambridge.